BEKA BA374C User manual

BA374C
Intrinsically safe
field mounting
indicating temperature
transmitter
Issue: 5
3rd December 2003

1. Description
2. Operation
2.1 Controls
3. Intrinsic Safety Certification
3.1 ATEX certificate
3.2 Other intrinsic safety certifications
3.3 Zones, Gas Groups and T rating
3.4 Certification information label
3.5 Input terminals 1, 2, 3 & 4
3.6 4/20mA output - Terminals 5 & 6
4. Electrical System Design for
Installations in Hazardous Areas
4.1 Using Zener barriers
4.2 Using galvanic isolators
5. Installation
5.1 Location
5.2 Installation procedure
5.3 EMC
6. Programming and calibration
6.1 Summary of programme menu
functions.
6.2 Description of programme menu
functions.
6.2.1 Transmitter input
6.3 For thermocouple inputs
6.3.1 Types of thermocouple
6.3.2 Display units
6.3.3 Display resolution
6.3.4 Cold junction compensation
6.3.5 Input open circuit drive
6.4 For resistance thermometer inputs
6.4.1 Type of resistance thermometer
6.4.2 Display units
6.4.3 Display resolution
6.5 For voltage inputs
6.5.1 Position of display decimal point
6.5.2 Low input & display calibration
6.5.3 High input & display calibration
6.6 4/20mA output current calibration
6.7 Security code
6.8 Calibrating the internal references
6.8.1 Conditioning internal references
6.8.2 Voltage input reference
6.8.3 3-wire RTD reference
6.8.4 4-wire RTD reference
6.8.5 Output current reference
7. Trim menu
7.1 Calibration procedure using trim menu
7.2 Periodic re-calibration using trim menu
8. Calibration example
9. Maintenance
9.1 Fault finding during commissioning
9.2 Fault finding after commissioning
9.3 Servicing
9.4 Routine maintenance
9.5 Guarantee
9.6 Customer comments
Accessories
10. Identification and mounting
10.1 Engraved scale and tag plates
10.2 Pipe mounting kits
10.3 Panel mounting kits
11. Alarms
11.1.1 Solid state output
11.1.2 Intrinsic safety
11.1.3 Programming and adjustment
11.2 Summary of programmable functions
11.3 Description of programmable functions
11.3.1 Alarm enable
11.3.2 Setpoint adjustment
11.3.3 Alarm function
11.3.4 Alarm output status
11.3.5 Hysteresis
11.3.6 Alarm delay
11.3.7 Alarm silence time
11.3.8 Access setpoint
11.4 Adjusting alarm setpoints from display
mode
12. Backlight
CONTENTS
The BA374C is CE marked to show compliance with the European Explosives Atmospheres
Directive 94/9/EC and the European EMC Directive 98/336/EEC

3
A Quick Guide to the Use of this Instruction Manual
Your BA374C has been factory set to the requirements specified on your purchase
order. If no requirements were given, the instrument will be supplied with default
settings i.e. 3 wire RTD input; high resolution display in °C; 4 to 20mA output
corresponding to an input and display of 0.0 to 100.0°C.
If the BA374C is set to your requirements before putting it into use you should
refer to:
Section 4 Electrical System Design
Section 5 Installation
Section 2.1 Controls
If optional alarms are fitted you should refer to Section 11.
You will also find the 'Trim' menu described in Section 7 useful if you wish to
calibrate the complete control loop.
If the BA374C has been supplied with default settings and you wish to change
these you will need to refer to:
Section 6 Programming and Calibration
This section explains the programme functions of the push-buttons and leads you
through the various stages of programming the unit. Among the sub-divisions of
Section 6 you will find information on setting up for:
Section 6.3 Thermocouple input
Section 6.4 Resistance thermometer input
Section 6.5 Voltage input
A word of warning: Section 6.8 explains how you can calibrate the instrument's
internal references. It is only necessary to carry out this operation if you will be
using these internal references to calibrate the instrument display, i.e not using an
external calibrator, and then only annual or less frequent adjustment is required. It
is not necessary to calibrate these references before putting the BA374C into
operation, we've already done that for you. For this reason the calibration section
of the programme menu is protected by an additional security code. You should
only enter this section of the programme if you are sure that you want to carry out
this calibration.
By following the notes in this manual you should be able to set up your BA374C
without any problem. However, If you do run into difficulties Section 9 provides
some guidance on typical problems you may find during commissioning. If you still
have difficulties please contact our Sales Department (01462 438301). Our Sales
Engineers will be able to talk you through the procedure.

4

1. DESCRIPTION
The BA374C is an intrinsically safe 4/20mA loop
powered transmitter incorporating a large easy to
read display. The instrument may be programmed
on-site to accept most common thermocouples
and resistance thermometers, and will provide a
linear 4/20mA output proportional to temperature,
plus a display in oC or oF. Voltage inputs may be
scaled allowing the BA374C to display variables
other than temperature.
Optional alarms provide two galvanically isolated
solid state outputs which may be independently
programmed for high or low operation. For
installations in poorly illuminated areas an optional
display backlight is available.
The BA374C transmitter has been designed in
accordance with EN50014 & EN50020, and has
been issued with an EC-Type Examination
Certificate confirming compliance with the
European ATEX Directive 94/9/EC.
The BA374C transmitter is available in a glass
reinforced polyester (GRP), or an epoxy painted
aluminium enclosure, both provide IP66 protection.
Fig 1 Simplified block diagram
2. OPERATION
Fig 1 shows a simplified block diagram of the
transmitter. The input signal, which may be from a
thermocouple, resistance thermometer or a dc
voltage, is digitised and transferred to the
instrument processor via an optical isolator. The
processor scales the signal and for temperature
measurement applies linearisation using look-up
tables stored in permanent memory. The
resulting temperature is shown on the internal
display and controls the 4/20mA output current.
The transmitter and the optional alarms are
powered from the 4/20mA current loop, but the
optional display backlight requires a separate
supply.
Each time power is applied to the instrument,
initialisation is performed. After a short delay the
following display sequence occurs:
-1.8.8.8.8 Display test in which all
segments of the display
are activated for 2.5
seconds.
. . . . For 1 second
0 For less than 0.5
seconds.
Input signal Using calibration
displayed information stored in
instrument memory.
2.1 Controls
All functions of the transmitter can be programmed
on-site via four push-buttons which are located
behind the enclosure cover - see Fig 5. In the
display mode i.e. when the transmitter is displaying
the input signal, these push-buttons have the
following functions. The 4/20mA output current is
not affected when these push-buttons are
operated, and when released, the input signal will
again be displayed.
Button Function
Down While this button is pushed the
transmitter will show the display
corresponding to a 4mA output.
Up While this button is pushed the
transmitter will show the display
corresponding to a 20mA output.
For transmitters fitted with alarms
E+Up While these buttons are pushed the
transmitter will display setpoint 1.
E+Down While these buttons are pushed the
transmitter will display setpoint 2.
It is also possible to adjust the two alarm setpoints
from the display mode - see section 11.4
5

3. INTRINSIC SAFETY CERTIFICATION
3.1 ATEX certificate
The BA374C has been issued with an EC-Type
Examination Certificate number
BAS02ATEX1185X by EECS showing compliance
with the European ATEX Directive 94/9/EC for
Group II, Category 1 gas atmospheres, EEx ia IIC
T5. The instrument bears the Community Mark
and, subject to local codes of practice, may be
installed in any of the European Economic Area
(EEA) countries. i.e. Austria, Belgium, Denmark,
Finland, France, Germany, Greece, Ireland, Italy,
Luxembourg, The Netherlands, Norway, Portugal,
Spain, Sweden and the United Kingdom. ATEX
certificates are also accepted in Norway, Iceland,
Liechtenstein, Switzerland and the Czech Republic
This manual describes installations which conform
with BS EN60079: Part 14:1997 Electrical
Installation in Hazardous Areas. When designing
systems for installation outside the UK, the local
Code of Practice should be consulted.
3.2 Other intrinsic safety certifications
Please contact BEKA for a list of non-European
intrinsic safety approvals.
3.3 Zones, Gas Groups and T rating
The BA374C and accessories have been certified
EEx ia IIC T5. When connected to an approved
system the transmitter may be installed in:
Zone 0 explosive gas air mixture
continuously present.
Zone 1 explosive gas air mixture likely
to occur in normal operation.
Zone 2 explosive gas air mixture not
likely to occur, and if it does,
it will only exist for a short time.
Be used with gases in groups:
Group A propane
Group B ethylene
Group C hydrogen
Having a temperature classification of:
T1 450oC
T2 300oC
T3 200oC
T4 135oC
T5 100oC
This allows the BA374C to be installed in all Zones
and to be used with most common industrial gases
at ambient temperatures between -40 & +60oC.
Note: minimum operating temperature -20oC.
3.4 Certification information label
The certification information label is fitted on the
top outside surface of the enclosure. The
instrument serial number and date of manufacture
are shown on a separate label inside the
enclosure.
3.5 Input terminals 1, 2, 3 & 4
When the BA374C is installed in a hazardous area
the input terminals may be connected to any
floating or earthed sensor complying with the
requirements for simple apparatus as defined in
Clause 5.4 of EN50020:1994. i.e. the sensor
generates less than 1.5V, 100mA, or 25mW.
Thermocouples and resistance thermometers are
simple apparatus and any floating or earthed
device may be connected to the BA374C,
providing that both are installed within the
hazardous area.
The permitted maximum parameters for the cables
connecting the transmitter to the sensor are 4µF
and 9.2mH in the most onerous gas group IIC
(hydrogen). These are large and are very unlikely
to be exceeded on any thermocouple or resistance
thermometer installation.
If the transmitter input is to be connected to a
device which does not comply with the
requirements for simple apparatus, a system
certificate should be obtained, or the safety of the
system assessed using the entity concept. The
certified safety description of the BA374C input
terminals is:
Uo = 8.61V
Io = 62mA dc
Po = 0.14W
3.6 4/20mA output - terminals 5 & 6
The BA374C transmitter is powered via these
terminals, and the current drawn is the 4/20mA
output signal. The transmitter is normally powered
from the safe area so a Zener barrier or galvanic
isolator is required to protect the circuit. Any
single channel Zener barrier or galvanic isolator
6

certified by an EEC approved body to [EEx ia] IIC
with output parameters equal to, or less than, those
shown below may be used.
Uo = 30V
Io = 280mA dc
Po = 0.85W
4. ELECTRICAL SYSTEM DESIGN FOR
INSTALLATION IN HAZARDOUS AREAS
4.1 Using Zener barriers
There are three basic requirements when
designing a loop incorporating the BA374C:
1. The intrinsic safety parameters of the Zener
barrier must be equal to or less than:
Uo = 30V
Io = 280mA
Po = 0.85W
2. The voltage between terminals 5 & 6 of the
BA374C must be between 10 and 30V.
3. The maximum supply voltage must not
exceed the maximum working voltage of the
Zener barrier.
Fig 2 illustrates the simplest configuration in which
a BA374C is powered from an isolated (floating)
power supply. Only one barrier is required as the
other wire is earthed at the barrier busbar.
Fig 2 BA374C powered from floating supply
If a common power supply is used to operate more
than one loop the negative side of the supply is
normally connected to earth. To enable the
negative side of the 4/20mA load also to be
earthed it is necessary to have a Zener barrier in
each wire going into the hazardous area as shown
in Fig 3. Any certified diode return barrier may be
used in the return wire. For guidance System
Certificate Ex96D2505 list some of these devices.
Fig 3 BA374C powered from a common supply
When designing any loop it is necessary to
establish that the sum of the voltage drops caused
by the BA374C transmitter, both Zener barriers,
the load and the cable resistance is less than the
minimum supply voltage.
For the transmitter loop shown in Fig 3:
Minimum operating voltage of BA374C 10.0V
Maximum voltage drop caused by 28V 6.8V
300ohm Zener barrier
(340ohms x 20mA)
Maximum voltage drop caused by 1.3V
diode return barrier
Maximum voltage drop caused by
250ohm load 5.0V
(250ohms x 20mA)
Maximum voltage drop caused by cable 0.2V
resistance (10ohms x 20mA)
-------
Total maximum voltage drop 23.3V
The power supply must therefore be above 23.3V,
but below the maximum working voltage of the
28V 300ohm Zener barrier which is typically 25.5V.
4.2 Using Galvanic Isolators
Galvanic isolators, although more expensive than
Zener barriers, do not require a high integrity earth
connection. For small systems where a high
integrity earth is not already available, the use of a
galvanic isolator often reduces overall installation
cost and will simplify the design of the loop.
Galvanic isolators also enable higher resistance
loads to be driven by the 4/20mA current.
7

Any EEx ia IIC certified galvanic isolator with
output safety parameters equal to or less than the
following may be used:
Uo = 30V
Io = 280mA
Po = 0.85W
For guidance, System Certificate Ex96D2506 lists
some of the devices which may be used.. Fig 4
shows a typical loop.
Fig 4 Typical application using galvanic isolators
5. INSTALLATION
The BA374C indicating temperature transmitter
should only be installed and operated by trained
competent personnel.
5.1 Location
The BA374C indicating transmitter can be supplied
in either a glass reinforced polyester (GRP), or an
epoxy painted aluminium enclosure. Both provide
IP66 protection and have a toughened glass
window and stainless steel fittings. The GRP
enclosure is suitable for most industrial installa-
tions including off-shore and waste water treatment
applications. For installations where solvents may
be present, the aluminium enclosure provides
maximum protection. The instrument should not
be installed in a position where it may be attacked
by aggressive substances.
The instrument must be positioned such that the
environmental conditions specified by the instru-
ment datasheet and the EC-Type Examination
Certificate are not exceeded.
Please consult BEKA associates if the instrument
is to be installed in an area subject to high
vibration.
Fig 5 BA374C installation procedure
Both enclosures are surface mounting, but may be
pipe or panel mounted using the accessory kits
described in section 10.
To simplify installation, the enclosure may be
installed and the field wiring terminated prior to the
transmitter assembly being fitted. Terminal 7 is
internally connected to the screen in the GRP
enclosure and to the case in the aluminium
enclosure.
5.2 Installation Procedure
Fig 5 illustrates the instrument installation
procedure.
a. Remove the enclosure cover by unscrewing
the four captive 'A' screws.
b. Remove the transmitter assembly from the
enclosure by unscrewing the three captive 'B'
screws and unplugging the flexible cable(s).
c. Mount the enclosure on a flat surface and
secure with screws or bolts through the four
corner 'C' holes. Alternatively use one of the
pipe or panel mounting kits described in
section 9.
d. Remove the temporary dust seals from the
cable entries and install the required glands,
conduit fittings or blanking plugs.
8

e. Connect the field wiring to the terminals as
shown in Fig 6.
f. Replace the transmitter assembly and evenly
tighten the three 'B' screws.
g. Replace the enclosure cover and evenly
tighten the four 'A' screws.
Fig 6 Dimensions and terminal connections
5.3 EMC
The BA374C complies with the requirements of the
European EMC Directive. For specified immunity
all wiring should be in screened twisted pairs.
6. PROGRAMMING AND CALIBRATION
The BA374C is programmed and calibrated via
four push-buttons which are located behind the
enclosure cover. All the functions are contained
in two easy to use menus, the Programme Menu
and the Trim Menu, which are shown diagramati-
cally in Figs 7A, 7B and 9.
The Programme Menu contains all the transmitter
parameters and enables calibration to be
performed against the internal transmitter
references.
The Trim Menu enables the transmitter display and
the 4/20mA output current to be calibrated against
an external standard, such as a voltage source or
temperature calibrator. This is the preferred
method of calibration A complete loop may be
calibrated using this menu to minimise errors
resulting from primary element and load
inaccuracies.
Each function in the programme menu is summa-
rised in section 6.1 and includes a cross reference
to more detailed information in the following
sections. Although this simple menu driven
system enables most adjustments to be made
without repeated reference to this manual, we
recommend that the summary of the programme
menu, calibration procedure using the trim menu
and the calibration example in sections 6.1, 7.1
and 8 are read prior to changing function or
calibrating the transmitter. Figs 7A, 7B and 9 show
the structure of the menus.
Details of the Trim Menu are contained in section 8
which also describes periodic calibration.
When the transmitter is fitted with alarms
additional functions are added to the programme
menu. These are described in section 11 of this
manual.
Throughout this manual push-buttons are shown in
italics e.g. P or Up push-button, and legends
displayed by the indicator are shown within
inverted commas e.g. 'CAL' and ' ALr2'.
Access to the programme menu is obtained by
operating the Pand Epush-buttons
simultaneously. If the transmitter is not protected
by a security code the first parameter 'InPut' will be
displayed. If the transmitter is protected by a
security code, 'COdE' will be displayed first.
Pressing Pagain will enable the security code to
be entered digit by digit using the Up and Down
buttons to change the flashing digit, and the P
push-button to move to the next digit. If the
correct code is entered pressing Ewill cause the
first parameter 'InPut' to be displayed. If an incor-
rect code is entered, or no button is pressed for ten
seconds, the transmitter will automatically return to
the operating mode.
When the transmitter is in the programme menu
the 4/20mA output current will remain locked at the
value prior to starting programming, and it will
therefore not respond to any input change.
However, calibration of the 4/20mA output via the
'CAL' function, or re-calibration of the 4/20mA
reference via the 'Cond' function will change the
output current.
9

Once within the programme menu the required
parameter can be reached by scrolling through the
functions using the Up and Down push-buttons as
shown in Figs 7A and 7B. When returning to the
display mode following changes to any
parameters, the transmitter will display four
decimal points for a few seconds while the new
information is stored in permanent memory.
All new BA374C indicators are supplied calibrated
as requested at the time of ordering. If calibration
is not requested, the transmitter will be set for 3
wire RTD input with 4 to 20mA output correspond-
ing to a display of 0.0°C to 100.0°C.
6.1 Summary of Programme Menu functions
The parameters which may be programmed vary
depending upon which input is selected. For:
Thermocouple and resistance
thermometer inputs
The BA374C transmitter will always display
sensor temperature. Programming allows the
display to be in degrees Centigrade or Fahren-
heit, and for the display resolution to be
selected.
Zero and span of the 4/20mA output current
may be programmed to represent any display
range.
Voltage input
The display may be programmed to show the
input voltage in any engineering units.
Zero and span of the 4/20mA output current
may be independently programmed to repre-
sent any displayed value.
Each of the functions in the programme menu is
described in the following summary with a cross
reference to more detailed information. Figs 7A
and 7B illustrates the location of each function
within the menu.
Display Summary of Programme Menu
functions
'InPut' Transmitter input
Conditions the transmitter to accept
thermocouple 'tHC', resistance
thermometer 'rtd' or a voltage 'UOLt'
input.
See section 6.2.1
For Thermocouple Inputs
Display Summary of Programme Menu
functions
'tYPE' Sensor type
Selects the type of thermocouple input.
See section 6.3.1
'dEg' Units of display
Sets display to oC or oF.
See section 6.3.2
'rESn' Display resolution
Selects low or high display resolution.
See section 6.3.3
'CJC' Cold junction compensation
Turns thermocouple cold junction
compensation ON or OFF.
See section 6.3.4
'burn' Input open circuit drive
Selects up scale drive, down scale
drive or no drive when input is open
circuit.
See section 6.3.5
For Resistance Thermometer Inputs
'tYPE' Sensor type
Selects 3-wire, 4-wire or differential
Pt100 resistance thermometer input.
See section 6.4.1
'dEg' Units of display
Sets display to oC or oF.
See section 6.4.2
'rESn' Display resolution
Selects low or high display resolution.
See section 6.4.3
For Voltage Inputs
''d.P.' Decimal point
Positions the dummy decimal point
between any of the display digits or
turns it off.
See section 6.5.1
'In-LO' Low input sub-menu
Enables the lower voltage input 'InPut'
and the corresponding display 'diSP' to
be defined.
See section 6.5.2
10

11

12

Display Summary of Programme Menu
functions
'In-HI' High input sub-menu
Enables the higher voltage input 'InPut'
and the corresponding display 'diSP' to
be defined.
See section 6.5.3
Other functions
'CAL' Calibration of 4/20mA output
This sub-menu defines the relationship
between the transmitter 4/20mA output
and the transmitter display. 'ZEro'
defines the display at which the output
is 4mA, and 'SPAn' the display at which
the output is 20mA.
See section 6.6
'Cond' Conditioning of internal references
WARNING!
This sub-menu is password
protected. It is not necessary
to carry out this operation
before putting the instrument
into service.
This sub-menu enables the internal
references to be calibrated against
external voltage, resistance and current
standards.
If the Trim Menu is used to calibrate the
transmitter, the internal references do
not require routine re-calibration.
See section 6.8
'COdE' Security code
Defines a four digit numeric code which
must be entered to gain access to the
programme and the trim menus.
Default code 0000 disables the security
function and allows unrestricted access
to all functions in the programme and
trim menus.
See section 6.7
6.2 Description of programme menu functions
This section contains a detailed description of each
function in the programme menu. It should be read
in conjunction with the summaries in section 6.1
and the programme structure shown in Figs 7A and
7B.
6.2.1 Transmitter input 'InPut'
This function conditions the transmitter to accept a
thermocouple 'tHC', resistance thermometer 'rtd'
or a voltage 'UOLt' input. To define the
transmitter input select 'InPut' from the programme
menu and press Pwhich will reveal the current
setting. This setting may be changed by scrolling
through the menu using the Up or Down buttons.
When the required input is displayed, pressing P
will reveal a sub-menu enabling the type of sensor
to be selected.
6.3 For thermocouple inputs
6.3.1 Type of thermocouple 'tYPE'
After selecting a thermocouple input, pressing P
will reveal the 'tYPE' sub-menu which contains
seven different thermocouples:
Type Display Standard
E E BS4937 Part 6 : 1974
J J BS4437 Part 3 : 1973
K h BS4437 Part 4 : 1973
N n BS4437 Part 8 : 1986
R r BS4937 Part 2 : 1973
T t BS4937 Part 5 : 1973
Pallaplat PALL Pfaulder BA302e
Pressing Pagain will display the current type of
thermocouple which may be changed by scroll
through the menu using the Up or Down buttons.
When the required type is displayed, press Eto
return to the sub-menu.
6.3.2 Display units 'dEg'
The transmitter display may be in degrees
centigrade or Fahrenheit. To check or change the
display units select 'dEg' from the sub-menu and
press Pto reveal the current setting. The setting
may be changed by pressing the Up or Down
button. When the required units is displayed, press
Eto return to the sub-menu.
6.3.3 Display resolution 'rESn'
The output of each type of thermocouple can be
displayed with high or low resolution as shown
below. Low resolution can improve the readability
of a noisy or rapidly changing display, but does not
degrade the performance of the 4/20mA analogue
output. High resolution is only available when the
transmitter is displaying temperature in oC. When
oF is selected the resolution is always one degree.
To check or change the display resolution select
'rESn' from the sub-menu and press Pto reveal
the current setting. The setting may be changed
by pressing the Up or Down button. When the
required resolution has been selected, press Eto
return to the sub-menu.
13

Display Resolution
Type Low (Lo) High (Hi)
E1
oC 0.1oC
J1
oC 0.1oC
K1
oC 0.2oC *
N1
oC 0.2oC *
R1
oC 0.4oC *
T1
oC 0.1oC
Pallaplat 1oC 0.2oC *
* Worst case high resolution figures are
quoted, at most temperatures resolution will
be greater.
6.3.4 Cold junction compensation 'CJC'
The temperature of the transmitter input terminals,
the thermocouple cold junction, is measured and
added to the output from the thermocouple so that
the transmitter displays and transmits the
temperature relative to zero degrees centigrade or
Fahrenheit. If cold junction compensation is not
required, e.g. for differential measurement with two
thermocouples, this function enables the cold
junction compensation to be turned off.
To turn the cold junction compensation on or off
select 'CJC' from the sub-menu and press Pto
reveal the current status. The setting may be
changed by pressing the Up or Down button. When
set as required press Eto return to the sub-menu .
6.3.5 Input open circuit drive 'burn'
If the thermocouple fails and becomes open circuit,
the transmitter can be conditioned to drive the
display and the 4/20mA output current up or down
into a safe condition. Alternatively the drive may
be turned off which will result in the display and the
4/20mA output current drifting towards zero.
To check or change the input open circuit drive
select 'burn' from the sub-menu and press Pto
reveal the current setting. The setting may be
changed by pressing the Up or Down button. When
the required setting has been selected, press Eto
return to the sub-menu.
6.4 For resistance thermometer inputs
6.4.1 Types of resistance thermometer 'tYPE'
The transmitter may be conditioned to accept
3-wire, 4-wire or differential Pt100 resistance
thermometers.
After selecting resistance thermometer input from
the 'InPut' sub-menu, press Pto reveal the 'tYPE'
sub-menu. Press Pagain to display the current
type of resistance thermometer which may be
changed by scrolling through the menu using the
Up or Down buttons. When the required type is
displayed, press Eto return to the sub-menu.
6.4.2 Display units 'dEg'
The transmitter display may be in degrees
centigrade or Fahrenheit. To check or change the
display units select 'dEg' from the sub-menu and
press Pto reveal the current setting. The setting
may be changed by pressing the Up or Down
button. When the required unit is displayed, press
Eto return to the sub-menu.
6.4.3 Display resolution 'rESn'
The output of the resistance thermometer can be
displayed with high or low resolution as shown
below. Low resolution can improve the readability
of a noisy or rapidly changing display, but does not
degrade the performance of the 4/20mA analogue
output. High resolution is only available when the
transmitter is displaying temperature in oC. When
oF is selected the display resolution is always one
degree.
To check or change the display resolution select
'rESn' from the sub-menu and press P to reveal
the current setting. The setting may be changed
by pressing the Up or Down button. When the
required resolution has been selected, press Eto
return to the sub-menu.
Display Resolution
Low High
1oC 0.1oC
6.5 For Voltage Inputs
When the transmitter is conditioned for a voltage
input both the input voltage range and the
corresponding display must be programmed.
6.5.1 Position of display decimal point 'd.P.'
A dummy decimal point can be positioned between
any of the display digits or it may be absent.
After selecting voltage input from the 'InPut' menu,
press Pto reveal the 'd.P.' sub-menu. Press P
again to display the current decimal point position.
The decimal point can be moved or turned off by
pressing the Up or Down push-button, followed by
Eto return to the sub-menu.
14

6.5.2 Low input & display calibration 'In-LO'
This function defines the lower voltage input and
the corresponding transmitter display. See
example below:
Input Transmitter
mV Display
-10.00 -3.000 Low input / display
12.55 3.765 High input / display
The calibration is performed using the internal
references and may be made with any transmitter
input voltage.
Select 'In-LO' from the menu and press Pwhich
will access a sub-menu containing two functions
'InPut' and ''dISP'.
Select the input voltage 'InPut' and press Pwhich
will cause the specified lower input millivoltage to
be displayed in the form XX.XX The flashing digit
of the input voltage can be changed by pressing
the Up or Down buttons. When the first digit is
correct, pressing Pwill transfer control to the next
digit. When the least significant digit has been
adjusted, press Eto return to the 'InPut' prompt,
from which the display prompt 'dISP' can be
selected by pressing the Up or Down button.
Pressing Pwill reveal the transmitter display
corresponding to the specified low input voltage.
The position of the dummy decimal point will be as
defined by function 'd.P.' - see section 6.5.1
The flashing digit of the display can be changed by
pressing the Up or Down buttons. When the first
digit is correct, pressing Pwill transfer control to
the next digit. When the least significant digit has
been adjusted, press Eto return to the ''dISP'
prompt.
6.5.3 High input & display calibration 'In-HI'
This function defines the higher voltage input and
the corresponding transmitter display. See
example below:
Input Transmitter
mV Display
-10.00 -3.000 Low input / display
12.55 3.765 High input / display
The calibration is performed using the internal
references and may be made with any transmitter
input voltage.
Select 'In-HI' from the menu and press Pwhich will
access a sub-menu containing two functions 'InPut'
and ''dISP'.
Select the input voltage 'InPut' and press Pwhich
will cause the specified higher input millivoltage to
be displayed in the form XX.XX The flashing digit
of the input voltage can be changed by pressing
the Up or Down buttons. When the first digit is
correct, pressing Pwill transfer control to the next
digit. When the least significant digit has been
adjusted, press Eto return to the 'InPut' prompt,
from which the display prompt 'dISP' can be
selected by pressing the Up or Down button.
Pressing Pwill reveal the transmitter display
corresponding to the specified higher input voltage.
The position of the dummy decimal point will be as
defined by function 'd.P.' - see section 6.5.1
The flashing digit of the display can be changed by
pressing the Up or Down buttons. When the first
digit is correct, pressing Pwill transfer control to
the next digit. When the least significant digit has
been adjusted, press Eto return to the ''dISP'
prompt.
6.6 4/20mA output current calibration 'CAL'
This sub-menu defines the relationship between
the transmitter display and the 4/20mA output
current. The transmitter output current is derived
from the transmitter display and will change if the
display calibration is changed. 'ZEro' defines the
display at which the output is 4mA, and 'SPAn' the
display at which the output is 20mA.
To calibrate the output current select 'CAL' from
the programme menu and press Pwhich will
access a sub-menu containing two functions.
Select 'ZEro' and press Pwhich will show the
transmitter display at which the output current is
4mA. The flashing digit of the display can be
changed by pressing the Up or Down buttons.
When the first digit is correct, pressing Pwill
transfer control to the next digit. When the least
significant digit has been adjusted, press Eto
return to the 'ZEro' prompt, from which the span
prompt 'SPAn' can be selected by pressing the Up
or Down button.
Press Pto show the transmitter display at which
the output current is 20mA. The flashing digit of
the display can be changed by pressing the Up or
Down buttons. When the first digit is correct,
pressing Pwill transfer control to the next digit.
When the least significant digit has been adjusted,
press Eto return to the 'SPAn' prompt.
Note: If a complete loop including a primary
element, BA374C temperature transmitter and a
load are being calibrated, the Trim Menu is the
preferred method. It allows the transmitter display
and output current to be adjusted to compensate
for inaccuracies in the other components in the
loop. Details of the trim menu are contained in
section 7 which also describes periodic calibration.
15

6.7 Security Code 'COdE'
Access to the Programme and Trim Menus may be
protected by a four digit numerical security code
which must be entered before access is granted.
New instruments are programmed with the default
security code 0000 which allows unrestricted
access to both menus.
To enter a new security code select 'COdE' from
the programme menu and press Pwhich will cause
the transmitter to display the current security code.
Each digit of the code can be changed using the
Up and Down push-buttons, and the P button to
move to the next digit. When the required code
has been entered press Eto return to the main
menu. The revised security code will be activated
when the transmitter is returned to the display
mode.
If the security code is lost, access to the
programme and trim menus can be obtained by
putting the security link in the override position -
see Fig 8. The security code can then be viewed
by selecting 'COdE' from the menu and pressing P.
Fig 8 Location of security code override link
6.8 Calibrating the internal references
WARNING!
Changing the internal references will
alter the instrument performance. Do
not attempt to recalibrate these
references unless you have adequate
test equipment and have read the
following instructions. For routine
calibration of the instrument use the
Trim Menu described in section 7.
If the internal references are used for calibrating
the BA374C transmitter they may require periodic
checking against external standards. Annual
checks will produce acceptable performance,
although less frequent checks are usually
adequate.
If the BA374C transmitter is calibrated against an
external voltage, resistance or temperature
calibrator using the trim menu, the internal
references should never need re-calibrating.
Details of the trim menu are contained in
section 7.
There are four internal references:
Voltage input
3-wire RTD
4-wire RTD
Current output
The input voltage reference must be adjusted first
irrespective of the transmitter application, but it is
only necessary to adjust the other three references
if the function to which they relate is being used.
For example, a BA374C with a thermocouple input
from which the 4/20mA output current is being
used would require the voltage input and the
current output reference adjusting.
6.8.1 Conditioning internal references: 'Cond'
WARNING!
Changing the internal references will
alter the instrument performance. Do
not attempt to recalibrate these
references unless you have adequate
test equipment and have read the
following instructions. For routine
calibration of the instrument use the
Trim Menu described in section 7.
These functions are contained in a protected
sub-menu to minimise the possibility of accidental
adjustment. Select 'Cond' from the menu and
press P. The transmitter will display '0000'. Using
the Up and Down buttons and the Pbutton to
move to the next digit enter the password 'SurE.
(Note that 'S' is entered as '5') There is a ten
second time-out on password entry. Pressing E
will then give access to the sub-menu containing
the four refences.
6.8.2 Voltage input reference 'U.IP'
With the BA374C input terminals connected to
accurate voltage calibrator, select 'U.IP' from the
'Cond' sub-menu and press P. The transmitter will
respond by displaying 'Lo' which is a request for an
accurate -75.000mV input. Adjust the external
voltage calibrator to supply -75.000mV and press
Pto store this figure in permanent memory. The
transmitter will display scrolling decimal points
while the reference is being updated and will then
return to the 'Lo' prompt.
Select 'Hi' from the sub-menu which is a request
for an accurate +75.000mV input. When the input
is correct press Pto store this figure in permanent
memory. The transmitter will display scrolling
decimal points while the reference is being
updated and will then return to the 'Hi' prompt.
This completes adjustment of the voltage input
reference.
16

6.8.3 3-wire RTD reference '3rtd'
This adjustment, which is only necessary if the
transmitter is used with a three wire resistance
thermometer, should be performed after the
voltage reference has been calibrated. To adjust
the 3-wire RTD reference the resistance
thermometer should be replaced by a 100 ohm
standard resistor or calibrator, with the
compensation loop remaining connected between
terminals 3 and 4. It is preferable to make this
substitution as close to the RTD as possible, but
transmitters may be calibrated in a workshop.
Select '3rtd' from the 'Cond' sub-menu and press
P. The transmitter will display scrolling decimal
points while the reference is being updated
followed by 'Ent' prior to returning to the '3rtd'
prompt. This completes adjustment of this
reference.
6.8.4 4-wire RTD reference '4rtd'
This adjustment, which is only necessary if the
transmitter is used with a four wire resistance
thermometer, should be performed after the
voltage reference has been calibrated. To adjust
the 4-wire RTD reference the resistance
thermometer should be replaced by a 100 ohm
standard resistor or calibrator, with both
compensation loops from terminals 1 and 4
connected at the standard resistor or calibrator. It
is preferable to make this substitution as close to
the RTD as possible, but if necessary the
transmitter may be calibrated in a workshop.
Select '4rtd' from the 'Cond' sub-menu and press
P. The transmitter will display scrolling decimal
points while the reference is being updated
followed by 'Ent' prior to returning to the '4rtd'
prompt. This completes adjustment of this
reference.
6.8.5 Output current reference 'OP'
Warning: ensure plant safety
before performing this adjustment
This adjustment is only necessary if the transmitter
4/20mA output current is used. A method of
accurately measuring the transmitter output
current, such as DVM, is required to calibrate this
reference.
Select 'OP' from the 'Cond' sub-menu and press P,
the transmitter will display 'SurE'. If it is safe to
change the transmitter output current between 4
and 20mA continue by pressing P. The transmitter
will display 'ZEro', pressing P again will change the
display to '.004A' and the transmitter output current
to approximately 4mA. The transmitter output
current shown on the external current measuring
instrument should be adjusted to 4.000 ±0.001mA
using the transmitter Up and Down buttons. When
correct press the E push-button to return to the
'ZEro' prompt.
To adjust the 20mA output current reference select
the 'SPAn' prompt by operating the Up or Down
button. Pressing Pwill change the display to
'.020A' and the transmitter output current to
approximately 20mA. The transmitter output
current shown on the external current measuring
instrument should be adjusted to 20.000± 0.001mA
using the transmitter Up and Down buttons.
When correct press the Epush-button twice to
return to the 'OP' prompt. This completes
adjustment of this reference.
7. TRIM MENU
The Trim Menu is the preferred method of routine
calibration. It enables the BA374C transmitter to be
adjusted using an external voltage, resistance or
temperature calibrator. For maximum accuracy
the complete loop including the thermocouple or
resistance thermometer may be calibrated by
heating or cooling the primary element.
Before using the Trim Menu all the functions in the
'InPut' and 'CAL' sections of the programme menu
must be defined, including the 4/20mA output
range. For voltage inputs, both the millivoltage
input and the corresponding display range must be
entered.
If a voltage calibrator is used to simulate a
thermocouple the transmitter cold junction
compensation must be turned off. Alternatively,
the temperature at the BA374C input terminals
may be measured and the voltage calibrator
corrected for ambient temperature, although this is
likely to produce less accurate results.
7.1 Calibration procedure using Trim Menu
The structure of the Trim Menu is shown in Fig 9.
Access to the menu is obtained by operating the P
and Down push-buttons simultaneously. If the
transmitter is not protected by a security code the
first parameter 'ZEro' will be displayed. If the
transmitter is protected by a security code, 'COdE'
will be displayed first. Pressing Pagain will enable
the security code to be entered digit by digit, using
the Up and Down buttons to change the flashing
digit, and the Ppush-button to move to the next
digit. If the correct code is entered pressing Ewill
cause the first parameter 'ZEro' to be displayed. If
an incorrect code is entered, or if no button is
pressed for ten seconds, the transmitter will
automatically return to the display mode.
17

Fig 9 Trim Menu
The 'ZEro' sub-menu allows the transmitter display
and output current to be independently trimmed at
the bottom of the input range. To make the adjust-
ment connect a calibrator to the transmitter input
terminals to simulate minimum input, or place the
primary element in a vessel at the minimum
temperature. With 'ZEro' displayed, pressing the P
push-button will cause the temperature display to
return. If the display does not correspond with the
input calibrator or the temperature of the primary
element, operate the Up or Down button until the
transmitter display is correct. Immediately the Up
or Down button is operated the annunicator in the
top left hand corner of the display will be activated
to warn that any changes in the input signal will be
ignored while this display correction is being made.
When the transmitter display is correct, press P
which will lock the transmitter display and, after
briefly displaying 'Ent', allow the 4/20mA output
current to be trimmed using the Up or Down push-
button. The output current should be measured
with an accurate DVM or another instrument within
the loop. Operate the Up or Down buttons until the
required output current is shown on the DVM or
other instrument. When correct, press the Ebutton
to store the trim correction in permanent memory
and return the BA374C transmitter to the 'ZEro'
prompt. This completes re-calibration of the
BA374C transmitter at minimum input.
The transmitter should now be re-calibrated at
maximum input by selecting the 'SPAn' sub-menu
and adjusting the calibrator to simulate maximum
input, or raising the primary element to maximum
temperature. With 'SPAn' displayed, pressing the
P push-button will cause the temperature display to
return. If the display does not correspond with the
input calibrator or the temperature of the primary
element, operate the Up or Down buttons until the
transmitter display is correct. Immediately the Up
or Down button is operated the annunicator in the
top left hand corner of the display will be activated
to warn that any changes in the input signal will be
ignored while this display correction is being made.
When the transmitter display is correct, press P
which will lock the transmitter display and, after
briefly displaying 'Ent', allow the 4/20mA output
current to be trimmed using the Up or Down push-
button. Again the output current should be
measured with an accurate DVM or another instru-
ment within the loop. Operate the Up or Down
buttons until the required output current is shown
on the DVM or other instrument. When correct,
press the Ebutton to store the trim correction in
permanent memory and return the BA374C trans-
mitter to the 'SPAn' prompt. This completes
re-calibration of the BA374C transmitter at
maximum input.
When calibrating the BA374C using the Trim Menu
both the zero and span must be adjusted.
The Trim Menu contains a clear function which
enables the small calibration correction made with
the 'ZEro' and 'SPAn' sub-menus to be removed.
To clear the corrections select 'CLr' from the trim
menu and press P. The display will show 'Ent' for
a short while and then return to the 'CLr' prompt.
7.2 Periodic re-calibration using Trim Menu
The trim menu is the best way of making small
calibration adjustments to compensate for any long
term drift which may occur. Initially an annual
check is recommended to achieve maximum
accuracy, although less frequent checks will
usually produce acceptable results.
If the BA374C internal references are used to
make frequent calibration changes, we
recommend that these references should be
initially checked once per year as described in
section 6.8 If the BA374C is always calibrated
with an external reference, such as a voltage
source using the trim menu, it will not be
necessary to check the internal reference.
18

8. CALIBRATION EXAMPLE
In this example a BA374C is required to display
with maximum resolution the temperature of a type
J thermocouple, and to transmit a 4/20mA signal
representing -10 to 240oC. If the thermocouple
breaks the 4/20mA output current is to rise to full
scale. The current security code is 1209.
The example is divided into two sections. Steps 1
to 10 explain how to condition the transmitter and
to calibrate the 4/20mA output using the internal
references. This will produce acceptable accuracy
for most applications, but will not compensate for
errors in the thermocouple or load connected to the
4/20mA output. Steps 11 to 13 describe how the
Trim Menu may be used to calibrate the complete
loop and to compensate for thermocouple errors.
Step 1 Initialisation
When power is applied to the loop the
BA374C will automatically perform the
initialisation routine described in section
2, and then display and transmit the
thermocouple temperature using the
existing calibration information.
Step 2 Enter the programme menu
Enter the programme menu by
simultaneously pressing the P and E
buttons. The transmitter will respond by
displaying 'COdE'. Press Pto clear this
prompt and set the display to the
security code 1209 using the Up, Down
and Ppush-buttons. Pressing Ewill
enter the code. After a few seconds
during which all the decimal points will
be activated, the first parameter 'InPut'
will be displayed.
Step 3 Define input
With 'InPut' displayed press Pwhich
will reveal the current transmitter
sensor type. Using the Up or Down
button scroll through the menu until
thermocouple input 'tHC' is displayed.
Step 4 Define type of thermocouple
With 'tHC' displayed press Pto enter
the thermocouple sub-menu. The first
parameter 'tYPE' will be displayed,
pressing P again will give access to
the seven different types of
thermocouple. Select 'J' using the Up
or Down button and then press Eto
return to the sub-menu.
Step 5 Define units of display
Using the Up or Down button select
'dEg', from the sub-menu and press P
to reveal the current units. Pressing
the Up or Down button will toggle
between oC and oF. Select oC and
press Eto return to the sub-menu.
Step 6 Resolution
Using the Up or Down button select
'rESn' from the sub-menu and press P.
Pressing the Up or Down button will
toggle between high and low resolution,
select 'Hi' and press E to return to the
sub-menu.
Step 7 Cold junction compensation
In this example only one thermocouple
is connected so cold junction
compensation is required. Using the
Up or Down button select 'CJC' from
the sub-menu and press P. The Up
and Down buttons will turn the cold
junction 'On' and 'OFF'. Select 'On' and
press E to return to the sub-menu.
Step 8 Input open circuit drive
Using the Up or Down button select
'burn' from the sub-menu and press P
to reveal the current status. Select 'uP'
using the Up or Down button and press
Ethree times to return to the 'InPut'
prompt via the 'burn' and 'tHC' prompts.
Step 9 Calibrating the 4/20mA output
'CAL' defines the display at which the
output current is 4mA and 20mA.
Select 'CAL' from the menu using the
Up or Down push-button, and enter the
sub-menu by pushing P. The
transmitter will display a 'ZEro' prompt
requesting the display at which the
output is to be 4mA. Press P and
enter -10.0 using the Up, Down and P
buttons. Press Eto return to the 'ZEro'
prompt. Select 'SPAn' from the
sub-menu and press P. Enter 240.0
which is the display at which the output
current is to be 20mA and press E twice
to return to the 'CAL' prompt.
19

Step 10 Return to the display mode
With the 'CAL' prompt displayed, press
Eto store the conditioning and
calibration information and return to the
operating mode. All the display
decimal points will be activated while
the information is being stored. This
completes the calibration of the
transmitter using the internal
references.
The following steps explain how, using the Trim
Menu, the BA374C transmitter may be calibrated
against an external reference, such as a voltage
source or temperature calibrator. Alternatively, the
complete loop including the primary element may
be calibrated by cooling and heating the
thermocouple to -10 and +240oC. This is the
preferred method for routine calibration.
Step 11 Entering the trim menu
Enter the trim menu by simultaneously
pressing the P and Down buttons - see
Fig 9. The transmitter will respond by
displaying 'COdE' . Press Pto clear
this prompt and set the display to the
security code 1209 using the Up, Down
and Ppush-buttons. Pressing Ewill
enter the code. After a few seconds
during which all the decimal points will
be activated, the first parameter 'ZEro'
will be displayed.
Step 12 Zero adjustment
This adjustment trims the display to
read exactly -10.0oC and the output
current to be exactly 4.000mA when the
type J thermocouple is at -10oC. This
can be achieved by cooling the
thermocouple to -10oC or by inputting
the voltage which the thermocouple
should theoretically produce. If a
voltage is used the transmitter cold
junction compensation (see section
6.3.4) should be turned off during the
calibration, or the input voltage should
be corrected for ambient temperature,
although this may be less accurate.
With the transmitter displaying the
'ZEro' prompt and the correct input
connected to the transmitter, push P
which will cause the transmitter to
display the thermocouple temperature.
Adjust the display with the Up and
Down buttons until it is -10.0
Note: Immediately the Up or Down
button is operated the annunicator in
the top left hand corner of the display
will be activated to warn that any
change in the input signal will be
ignored while this display correction is
being made.
Operating the P push-button will lock
the transmitter display at -10.0 and
allow the output current to be trimmed
using the Up or Down button. When
the output current measured by a DVM
is 4.000mA, the Epush-button should
be operated to return the transmitter to
the 'ZEro' prompt.
This completes calibration at -10.0oC.
Step 13 Span adjustment
With the transmitter displaying the
'ZEro' prompt select 'SPAn' by pressing
the Up or Down button. With the
thermocouple heated to 240oC, or an
equivalent voltage input, push Pwhich
will cause the transmitter to display the
thermocouple temperature. Adjust the
display with the Up and Down buttons
until it is 240.0
Note: Immediately the Up or Down
button is operated the annunicator in
the top left hand corner of the display
will be activated to warn that any
change in the input signal will be
ignored while this display correction is
being made.
Operating the P push-button will lock
the transmitter display at 240.0 and
allow the output current to be trimmed
using the Up or Down button. When
the output current measured by a DVM
is 20.000mA, the Epush-button should
be operated to return the transmitter to
the 'SPAn' prompt.
This completes calibration at 240.0oC.
Pressing the E push-button again will
return the transmitter to the display
mode.
20