BEKA BA374NC User manual

BA374NC
Type nL certified
field mounting
indicating temperature
transmitter
Issue: 5
3rd December 2003

1. Description
2. Operation
2.1 Controls
3. Type n Certification
3.1 Certificate of Assurance
3.2 ATEX certification
3.3 Zones, gas groups & T ratings
3.4 Certification label information
4. Electrical System Design for
Installations in Hazardous Areas
5. Installation
5.1 Location
5.2 Installation in Zone 2 hazardous area
5.3 Installation procedure
5.4 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 kit
11. Alarms
11.1.1 Solid state output
11.1.2 Type n certification
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 BA374NC is CE marked to show compliance with the European Explosive 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 BA374NC 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 BA374NC 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 BA374NC 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 unit 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 BA374NC without any
problem. If you do run into difficulties however Section 9 (Maintenance) 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 BA374NC is an Ex n certified 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 BA374NC to display variables
other than temperature.
Optional alarms provide two galvanically isolated
solid state outputs which may be independently
programmed as high or low trips. For installations
in poorly illuminated areas an optional display
backlight is available.
The instrument has been certified Ex N IIC T5 by
BASEEFA to BS6941:1988. In addition the
instrument complies with the European ATEX
Directive 94/9/EC for Group II Category 3G
equipment. This allows it to be installed in a Zone
2 hazardous area without the need for Zener
barriers, galvanic isolators or additional
mechanical protection.
The BA374NC 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. The
4/20mA output current is proportional to the
displayed temperature.
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 Figs 5A and
5B. 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 by operating these
push-buttons, 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. TYPE 'n' CERTIFICATION
3.1 Certificate of Assurance
BASEEFA has issued the BA374NC with a
Certificate of Assurance BAS No. 96Y4522
confirming compliance with BS6941:1988. This
verifies that in normal operation the BA374NC is
not capable of igniting a surrounding explosive
atmosphere, and a fault capable of causing ignition
is not likely to occur.
3.2 ATEX certification
The BA374NC complies with the European ATEX
Directive 94/9/EC for Group II, Category 3G
equipment. It has been assessed using the
'Internal Control of Production' procedure specified
in Annex 8 of the Directive. A Technical Dossier
has been prepared and a EC Declaration of
Conformity number N0014 has been issued.
The instrument bears the Community Mark and,
subject to local codes of practice, may be installed
in any of the European Economic Area (EEA)
member countries. i.e. Austria, Belgium,
Denmark, Finland, France, Germany, Greece,
Ireland, Italy, Luxembourg, The Netherlands,
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:Part14:1997
Electrical Installation in Hazardous Areas. When
designing systems for installation outside the UK,
the local code of practice should be consulted.
3.3 Zones, gas groups and T rating
The BA324NC has an EEx nL IIC T5, Tamb -40 to
60oC safety code as defined in BS EN50021:1999
Electrical apparatus for potentially explosive
atmospheres - Type of protection 'n'.
'L' indicates that the BA374NC uses an
energy-limiting technique to achieve compliance
as defined in Clause 21 of BS EN50021:1999.
This technique is based on the philosophy of
intrinsic safety which limits the current and voltage
applied to components which may generate a
spark in normal operation e.g. switches and
switches and potentiometers.
These approvals confirm that the BA374NC is
'safe in normal operation' and may be installed in:
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 BA374NC to be installed in Zone 2
and to be used with most common industrial
gases.
3.4 Certification label information
Certification information is shown on a label fitted
in a recess on the top outer surface of the
enclosure. It shows the ATEX certification
information and the Certificate of Assurance with
BS6941:1988. The instrument serial number and
date of manufacture are shown on a separate label
within the enclosure.
4. ELECTRICAL SYSTEM DESIGN FOR
INSTALLATION IN HAZARDOUS AREAS
There are two basic requirements when designing
a loop incorporating a BA374NC:
1. To comply with the EEx nL certification, in
normal operation i.e. without any faults, the
safe area power supply must have an output
voltage of less than 30V.
The safety compents within the BA374NC
will automatically ensure that the output
current does not exceed 25mA in normal
operation.
2. To ensure correct operation of the
transmitter the voltage between terminals 5
& 6 of the BA374NC must be between 10
and 30V at all output currents.
Fig 2 illustrates a typical temperature measuring
loop. The BA374NC is located in Zone 2 and
powered from a supply in the safe area.
WARNING
The enclosure cover should only be
removed when the measurement loop
is not energised, or when there is no
risk of a flammable atmosphere being
present and dust or water can not enter
the enclosure. Before replacing the
enclosure cover ensure that the sealing
gasket is undamaged and is free from
dirt and foreign bodies.
6

Fig 2 BA374NC powered from floating supply
The sum of the maximum voltage drops of all the
components in the loop must be less than the
minimum power supply voltage.
Minimum operating voltage of BA374NC10.0V
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 15.2V
Therefore in this example the power supply must
have an output of greater than 15.2V
5. INSTALLATION
5.1 Location
The BA374NC 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 polycar-
bonate window and stainless steel fittings. The
GRP enclosure is suitable for most industrial instal-
lations including off-shore and waste water treat-
ment applications. For installations where solvents
may be present, the aluminium enclosure provides
maximum protection. Both enclosures are surface
mounting, but may be pipe or panel mounted using
the accessory kits described in section 10.
Fig 3 BA374NC installation procedure
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 in Zone 2 hazardous areas
Installations within a Zone 2 hazardous area must
comply with the requirements of BS
EN60079:1997 Part 14. Both of the instrument
cable entries must be fitted with EEx n or EEx e
approved glands or blanking plugs.
The BA374NC has galvanic input to output
isolation. This allows an earthed thermocouple or
resistance thermometer to be used providing the
field wiring is able to withstand a 500V rms
insulation test for one minute
5.3 Installation Procedure
Fig 3 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).
7

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
sections 10.2 and 10.3.
d. Remove the temporary dust seals from the
cable entries and install the required glands,
conduit fittings or blanking plugs.
e. Connect the field wiring to the terminals as
shown in Fig 4.
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 4 Dimensions and terminal connections
5.4 EMC
The BA374NC 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 BA374NC 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 5A, 5B and 7.
The Programme Menu contains all the transmitter
parameters and enables calibration to be
performed against the internal transmitter refer-
ences.
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. 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 5A, 5B and 7 show
the structure of both menus.
Details of the Trim Menu are contained in section 7
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.
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.
8

9

10

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.
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 5A and 5B. 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 BA374NC indicators are supplied
calibrated as requested at the time of ordering. If
calibration is not requested, the transmitter will
have default calibration i.e. 3 wire RTD input; high
resolution display in °C; 4 to 20mA output corre-
sponding to an input and display of 0.0 to 100.0°C.
11

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 BA374NC 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 5A
and 5B 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
'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
Display Summary of Programme Menu
functions
'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
'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
12

Other functions
Display Summary of Programme Menu
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. It is normally only
necessary to use this function once per
year.
If the Trim Menu is used to calibrate the
transmitter, the internal references do
not require 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 5A and
5B.
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 from which, for
thermocouple and resistance thermometer inputs,
the type of sensor may be selected and associated
parameters programmed.
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 are 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.
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 *
13

* 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,
which is 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 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 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.
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
14

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, BA374NC 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.
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 6. The security code can then be viewed
15

by selecting 'COdE' from the menu and pressing
P.
Fig 6 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 BA374NC transmitter they may require periodic
checking against external standards. Annual
checks will produce acceptable performance,
although less frequent checks are usually
adequate.
If the BA374NC 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 BA374NC 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 references.
6.8.2 Voltage input reference 'U.IP'
With the BA374NC input terminals connected to an
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. 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 '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.
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'
16

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 a 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 BA374NC 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, and for voltage inputs the input and display
ranges.
If a voltage calibrator is used to simulate a
thermocouple the transmitter cold junction
compensation must be turned off. Alternatively,
the temperature at the BA374NC 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 7.
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 7 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 annunciator 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 BA374NC transmitter to the 'ZEro'
prompt. This completes re-calibration of the
BA374NC 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 annunciator 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 BA374NC
transmitter to the 'SPAn' prompt. This completes
re-calibration of the BA374NC transmitter at
maximum input.
When calibrating the BA374NC using the Trim
Menu both the zero and span must be adjusted.
The Trim Menu contains a clear function 'CLr'
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 BA374NC internal references are used to
make frequent calibration changes, we
recommend that these references should be
initially checked once per year as described in
sections 6.8.1 to 6.8.5 If the BA374NC 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 BA374NC 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
BA374NC 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 BA374NC 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.
Step 11 Entering the Trim Menu
Enter the Trim Menu by simultaneously
pressing the P and Down buttons - see
Fig 7. 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 annunciator 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 annunciator 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