Ahlborn ALMEMO 2490-1A User manual

____________________________
Operating instructions
English
Universal measuring instruments
ALMEMO® 2490-1A, 2490-2A
V2.9
04.11.2021
www.ahlborn.com

2
1. OPERATING CONTROLS
(1) Measuring inputs M0 and M1
M0 ... M1 for all ALMEMO®sensors
M2 Function channel, differential
M10...M32 9 additional channels
(2) unavailable
(3) Outputs A1, A2
A1 Interface USB (ZA 19019-DKU)
RS 232 (ZA 1909-DK5)
Optic fiber (ZA 1909-DKL)
Ethernet (ZA 1945-DK)
2nd analog output (ZA 1601-RK)
A2 Network cable (ZA1999-NK5/NKL)
Trigger input (ZA 1000-ET/EK)
Relay outputs (ZA 1006-EAK)
1st analog output (ZA 1601-RK)
(4) Connection DC 12V
Mains adapter (ZA1312-NAx, 12V, min.1 A)
Cable, electr. isol. (ZA2690-UK, 12V)
ALMEMO® connector (ZA1000-FSV)
(5) LCD
(a) Function
(b) Measuring point, 2nd meas. value
(c) Units for 2nd measured value
(d) Units for 1st measured value
(e) 1st measured value
(f) Operational states
LOBAT Battery voltage <3.3 V
FREE Unlocked for adjust. purposes
CORR Measured value corrected
REL Relative measuring
(6) Operating keys
ON OFF Switch the device on
To switch device OFF,
press and hold down
M▲ , M▼ Meas. point selection
MAX , MIN Max. / min. value
clear: press and hold down
MEM Measured value memory
press and hold down: value displaying
CLR Relative measuring
Sensor adjustment
cancel: press and hold down
Rear of device
(7) Battery compartment
3 AA alkaline-manganese batteries

3
2. CONTENTS
1. Operating controls ......................................................................................2
2. Contents .....................................................................................................3
3. General.......................................................................................................5
3.1 Warranty.............................................................................................5
3.2 Scope of delivery ...............................................................................6
3.3 Waste disposal...................................................................................6
4. Safety instructions ......................................................................................7
4.1 Special notes on use .........................................................................8
4.2 Handling batteries / rechargeable batteries correctly ........................8
5. Introduction.................................................................................................9
5.1 Functions ...........................................................................................9
5.1.1 Sensor programming .....................................................................9
5.1.2 Measuring operations .................................................................. 11
5.1.3 Process control ............................................................................12
6. Initial commissioning ................................................................................13
7. Power supply ............................................................................................14
7.1 Battery operation and ......................................................................14
7.2 Mains operation ...............................................................................14
7.3 External DC voltage supply .............................................................14
7.4 Sensor supply ..................................................................................14
7.5 Switching ON / OFF, ........................................................................14
7.6 Data buffering ..................................................................................15
8. Connecting the transducers......................................................................16
8.1 Transducers .....................................................................................16
8.2 Measuring inputs and additional channels ......................................16
8.3 Potential separation .........................................................................17
9. Display and keypad ..................................................................................18
9.1 Display .............................................................................................18
9.2 Keypad.............................................................................................19
10. Measuring operations ..........................................................................20
10.1 Measured value ...............................................................................20
10.1.1 Selecting a measuring point ....................................................20

2. Contents
4
10.1.2 Measuring ranges ....................................................................20
10.1.3 Double display .........................................................................22
10.2 Peak value memory .........................................................................22
10.3 Measured value memory .................................................................23
10.4 Relative measuring ..........................................................................24
10.5 Sensor adjustment ...........................................................................24
10.6 Differential measurement.................................................................25
11. Outputs ................................................................................................26
11.1 Interface ...........................................................................................26
11.2 Analog outputs .................................................................................26
12. Device configuration ............................................................................27
12.1 Device address and networking.......................................................27
12.2 Analog output...................................................................................27
12.3 Automatic switch OFF......................................................................28
12.4 Device locking..................................................................................28
12.5 Atmospheric pressure compensation ..............................................29
13. Trouble-shooting ..................................................................................30
14. Declaration of conformity .....................................................................32
15. Appendix ..............................................................................................33
15.1 Technical data ..................................................................................33
15.2 Product overview .............................................................................34
15.3 Index ................................................................................................35
Your contact .....................................................................................................36

5
3. GENERAL
Congratulations on your purchase of this new and innovative ALMEMO® meas-
uring instrument. Thanks to the patented ALMEMO® connector the device con-
figures itself automatically; its operation should be fairly straightforward. The de-
vice can, however, be used with such a wide range of sensors and peripherals
and offers many different special functions. You are advised therefore to
properly familiarize yourself with the way the sensors function and with the de-
vice's numerous possibilities and take the time to carefully read these operating
instructions and the appropriate sections in the ALMEMO® Manual. This is ab-
solutely necessary to avoid operating and measuring errors and to prevent dam-
age to the device. To help you find the answers to your questions quickly and
easily there is a comprehensive index at the end both of these instructions and
of the Manual.
3.1 Warranty
Each and every device, before leaving our factory, undergoes numerous quality
tests. We provide a warranty, lasting two years from delivery date, that your
device will function trouble-free. Before you send your device to us, please ob-
serve the advisory notes in Chapter 13. Trouble-shooting In the unlikely event
that the device proves defective and you need to return it please wherever pos-
sible use the original packaging material for dispatch and enclose a clear and
informative description of the fault and of the conditions in which it occurs.
This warranty will not apply in the following cases :
⚫The customer attempts any form of unauthorized tampering and alteration
inside the device.
⚫The device is used in environments and conditions for which it is not suited.
⚫The device is used with unsuitable power supply equipment and / or periph-
erals.
⚫The device is used for any purpose other than that for which it is intended.
⚫The device is damaged by electrostatic discharge or lightning.
⚫The user fails to observe and comply with the operating instructions.
The manufacturer reserves the right to change the product's characteristics in
the light of technical progress or to benefit from the introduction of new compo-
nents.

3. General
6
3.2 Scope of delivery
When you unpack the device check carefully for any signs of transport damage
and ensure that delivery is complete.
Measuring instrument ALMEMO® 2490A with 3 AA alkaline batteries
These operating instructions
ALMEMO® Manual
CD with the ALMEMO® Control software and various useful accessories
In the event of transport damage please retain the packaging material and in-
form your supplier immediately.
3.3 Waste disposal
The pictogram showing a waste bin crossed through means
that the product is subject to European Union regulations on
segregated waste disposal. This applies both to the product
itself and to any accessories marked with the same symbol.
Disposal of any such item as unsorted domestic waste is
strictly forbidden
•Please dispose of all packaging materials according to the applicable national
waste management regulations.
•Please dispose of cardboard boxes, protective plastic packaging materials,
and all preservative substances separately and in the proper manner.
•The disposal of the device itself (also of device parts, accessories, and con-
sumables) is subject to the applicable national and local waste management
regulations and to the environmental protection legislation in force in the coun-
try of use.
•Please dispose of all waste in the proper manner;
this applies in particular to all parts and substances that constitute a hazard
for the environment. This includes inter alia plastics, batteries, and recharge-
able battery packs .
•When disposing of goods, please wherever possible use the original packag-
ing materials.

7
4. SAFETY INSTRUCTIONS
DANGER
Danger to life and limb, risk of damage to equipment
Read the instructions carefully before starting to operate
the device.
Please ensure that you comply with all general safety advice
and the special safety instructions included in other chap-
ters.
Such risks may occur in the following circumstances :
•Failure to heed the operating instructions and all the safety notes
these contain
•Any form of unauthorized tampering or alteration inside the de-
vice
•Use of the device in environments or conditions for which it is not
suited
•Use of the device with an unsuitable power supply and / or in
conjunction with unsuitable peripheral equipment
•Use of the device for any purpose other than that for which it is
intended
•Damage caused by electrostatic discharge or lightning.
DANGER
Risk of fatal injury caused by dangerously high voltage
Such risks may occur in the following circumstances :
•Use of the device with an unsuitable power supply and / or in
conjunction with unsuitable peripheral equipment
•Damage caused by electrostatic discharge or lightning
•Do not run sensor lines in the vicinity of high-voltage power ca-
bles.
•Before you touch any sensor lines, ensure that all static electric-
ity has been discharged.
DANGER
Warning - explosive atmospheres or substances
In the vicinity of various fuels or chemicals there is a risk of ex-
plosion.
Do not use the device in the close vicinity of blasting work or
filling stations!

4. Safety instructions
8
4.1 Special notes on use
•If the device is brought into the work-room from a cold environment
there is a risk that condensation might form on the electronics. In meas-
uring operations involving thermocouples pronounced changes in tem-
perature may cause substantial measuring errors. You are advised
therefore to wait until the device has adjusted to the ambient tempera-
ture before starting to use it.
•Before using the mains adapter make sure that the mains voltage is
suitable.
•Be sure to observe the maximum load capacity of the sensor power
supply.
•Sensors with their own integrated power supply are not electrically iso-
lated from one another
4.2 Handling batteries / rechargeable batteries cor-
rectly
When inserting batteries / rechargeable batteries ensure that
these are correctly polarized.
If the device will probably not be needed for a relatively long pe-
riod of time or if the batteries are empty, remove the batteries; this
will prevent battery acid leaking onto the device and damaging it.
Rechargeable batteries should be recharged as and when nec-
essary.
You should never attempt to recharge an ordinary (non-recharge-
able) battery; it may explode !
Batteries / rechargeable batteries must never be short-circuited
or thrown onto the fire.
Batteries / rechargeable batteries are special waste and must not
be discarded together with normal domestic waste.

9
5. INTRODUCTION
The ALMEMO® 2490A is a new member in our family of unique measuring de-
vices - all equipped with Ahlborn's patented ALMEMO® connector system. The
intelligent ALMEMO® connector offers decisive advantages when connecting
sensors and peripherals because all parameters are stored in an EEPROM lo-
cated on the connector itself; repeat programming is thus no longer necessary.
All sensors and output modules can be connected to all ALMEMO® measuring
instruments in the same way. Programming and functioning are identical for all
units. The following points apply to all devices in the ALMEMO® measuring sys-
tem; these are described in detail in the ALMEMO® Manual which is included in
delivery with each device.
Detailed explanation of the ALMEMO® system (Manual Ch 1)
Overview of the device functions and measuring ranges (Manual Ch 2)
Basic principles, operation, and technical data for all sensors (Manual Ch 3)
Options for connecting your own existing sensors (Manual Ch 4)
All analog and digital output modules (Manual Section 5.1)
Interface modules USB, RS232, optic fiber (Manual Section 5.2)
The whole ALMEMO® networking system (Manual Section 5.3)
All functions and their operation via the interface (Manual Ch 6)
Complete list of interface commands with all the printouts (Manual Ch 7)
The operating instructions you are now reading cover only those features and
controls that are specific to this device. Many sections therefore also refer to the
more detailed description in the Manual; (see Manual, Section xxx).
5.1 Functions
The ALMEMO® 2490-1A has one electrically isolated measuring input suitable
for all ALMEMO® sensors; the 2490-2A has two such measuring inputs. The
measuring possibilities are virtually unlimited; there are 4 channels per sensor
connector and 4 device-internal function channels (type -2 only) - with over 70
measuring ranges. For operation purposes the device incorporates a large LCD
display and a keypad. An option is available with an internal electrically isolated
analog output including a DC socket for a mains adapter (socket P0). The stand-
ard version with interface has three output sockets, namely A1 and A2, suitable
for all ALMEMO® output modules, e.g. analog outputs, digital interfaces, trigger
and relay cables, plus a DC socket for a mains adapter. Several devices can be
networked by simply linking them together via cable.
5.1.1 Sensor programming
The measuring channels are programmed, completely and automatically, by the
ALMEMO® connectors. The user can freely supplement or modify this program-
ming; this applies to the interface version only. However, devices without the
interface also behave according to all the programmed parameters.
Measuring ranges
Appropriate measuring ranges are available for all sensors with a non-linear

5. Introduction
10
characteristic, e.g. 10 thermocouple types, NTC and PT100 probes, infrared
sensors, and flow transducers (rotating vanes, thermoanemometers, Pitot
tubes). For humidity sensors additional function channels are available for cal-
culating humidity variables such as dew point, mixture ratio, vapor pressure, and
enthalpy. Even complex chemical sensors are supported. Measured values from
other sensors can also be acquired using the voltage, current, and resistance
ranges with individual scaling in the connector. Existing sensors can also be
used - so long as the appropriate ALMEMO® connector is connected via its
screw terminals. For digital input signals, frequencies, and pulses, adapter con-
nectors are available with an integrated microcontroller. It is thus possible to
connect virtually any sensor to any ALMEMO® measuring instrument and to
change sensors without the need for any extra settings.
Function channels
Maximum, minimum, average, and differential values from certain measuring
points can be programmed as function channels, also internal channels, and
can be processed like normal measuring points.
Units
The 2-character units display can be adapted for each measuring channel so
that both the display and via interface always indicate the correct units, e.g.
when a transmitter is connected. Conversion between °C (Centigrade) and °F
(Fahrenheit) is performed automatically.
Measured value designation
Each sensor is identified by means of a 10-character alphanumeric name. This
name is entered via the interface and will appear via interface and in the soft-
ware.
Correction of measured values
The measured value on each measuring channel can be corrected both in terms
of zero-point and gain; this means that even sensors usually requiring initial ad-
justment (e.g. expansion, force, pH) can be freely interchanged. Zero-point cor-
rection and, partly at least, gain adjustment can be performed at the touch of a
button. Sensors with multi-point calibration can also be connected; (see Manual
Section 6.3.13).
Scaling
The corrected measured value on each measuring channel can also be further
scaled in terms of zero-point and gain - using the base value and factor. The dec-
imal point position can be set by means of the exponent function.
Limit values and alarm
Per measuring channel two limit values can be set (1 maximum and 1 minimum).
In the event of one of these limit values being exceeded relay output modules
actuate the associated alarm contacts; these can be allocated individually to
specific limit values. Hysteresis is set by default to 10 digits but this can be ad-
justed to any number between 0 and 99. The exceeding of a limit value can also
be used to start or stop measured value recording automatically.

5. Introduction
11
Sensor locking
All sensor data stored in the connector EEPROM can be protected by means of
a graduated locking function against undesired access.
5.1.2 Measuring operations
For each transducer up to 4 measuring channels are available; i.e. it is also
possible to evaluate double sensors, individually scaled sensors, and sensors
with function channels. You can move forwards or backwards from one meas-
uring channel to the next using the keypad. The selected measuring point is by
default assigned preferred status and is scanned at half the measuring rate; all
other active channels are also scanned but in the background (semi-continuous
mode). The data is output on the display and, if available, to an analog output.
To shorten the response time when there are several measuring points the
measuring rate can be set to continuous and increased accordingly.
Measured values
The measured value for the selected measuring point is shown continuously
with autozero and, as and when necessary, with measured value correction.
With most sensors, sensor breakage is detected automatically (except for con-
nectors with shunt, dividers, or additional electronics).
Analog output and scaling
Each measuring point can be scaled by means of analog start and analog end
in such a way that the measuring range thus defined covers the full range of the
analog output (2 V, 10 V, or 20 mA). At the analog output the device can output
the measured value from any measuring point or a programmed value.
Measuring functions
With some sensors, to achieve optimal measured value acquisition, certain special
measuring functions are required. Cold junction compensation is provided for ther-
mocouples; temperature compensation is provided for dynamic pressure, pH, and
conductivity probes; and atmospheric pressure compensation is provided for humid-
ity sensors, dynamic pressure sensors, and O2 sensors.
Measured value smoothing
Measured values of an unstable or strongly fluctuating nature can be smoothed
by means of a sliding average over a number of values programmable from 2 to
99.
Maximum and minimum values
For each measuring operation the maximum value and minimum value are ac-
quired and saved to memory. These values can then be displayed, output, or
deleted from memory.
Measured value memory
Up to 100 measured values can be saved manually. This data can then be
shown on the display or output via the interface.
Differential measurement
It is possible, by setting the measured value to zero, to perform relative meas-
uring operations with respect to a reference value; with 2 sensors and the same

5. Introduction
12
measured variables genuine differential measuring operations can be per-
formed.
5.1.3 Process control
(interface functions, see Manual Ch 6, not type L)
To record the measured values from all connected sensors in digital form meas-
uring point scanning is performed continuously with measured value output ac-
cording to a time-based process control. This may be per cycle or, if really rapid
results are required, at the measuring rate itself. The measuring operation can
be started and stopped via the interface by means of an external trigger signal
or by a specified limit value being exceeded.
Date and time-of-day
Date and time-of-day can be freely set and then used in the logging of measur-
ing operations. When the batteries are replaced these date and time-of-day set-
tings are lost and have to be reset.
Cycle
The cycle can be programmed to any value between 00:00:01 (1 second) and
59:59:59 hh:mm:ss. This function permits cyclic output of measured values to
the interfaces and cyclic calculation of average values.
Print cycle factor
The print cycle factor can be used to limit data output from particular channels;
this may be necessary in order to reduce excessive data flow especially while
data is being saved.
Averaging over measuring point scans
The measured values from measuring point scans can be averaged either over
the whole measuring duration or over the specified cycle. These average values
can then be output and saved on a cyclic basis to function channels provided
for this purpose.
Measuring rate
All measuring points are scanned at the measuring rate (2.5 or 10 mops). To
accelerate recording it is also possible to output all measured values at this
measuring rate via the interface.
Control outputs
Output relays and analog outputs can be individually addressed via the inter-
face.
Output
All data logs, measured values, and programming parameters can be output to
any peripheral equipment. RS232, RS422, USB, and Ethernet interfaces are
available using the appropriate interface cables. Measured data can be output
in list, column, or table format. Files in table format can be processed directly
using any standard spreadsheet software. The print header can be programmed
to refer specifically to your company or to your application.
Networking
All ALMEMO® devices can be addressed and can be easily networked by
simply linking them together via network cable.

6. Initial commissioning
13
Software
Each ALMEMO® Manual is accompanied by the AMR-Control software pack-
age, which can be used to configure the measuring instrument, to program the
sensors, and to read out from the measured value memory. Using the integrated
terminal, measuring operations can also be performed online. The WINDOWS®
software package WIN-Control is provided for the purposes of measured value
acquisition via networked devices, for graphical presentation, and for more com-
plex data processing.
6. INITIAL COMMISSIONING
1. Connect sensor to socket M0 (1); see 8.
2. Ensure that the power supply is provided via 3 AA batteries or mains adapter;
3. Switch ON by pressing key ON (6) ; see 7.5.
4. Select measuring channels by pressing key M▲ (6), read out measured
values (5e); see 10.1.1.
5. Save the measured value by pressing key MEM (6) see 10.3.
6. Relative measuring with respect to a reference value or sensor adjustment
by pressing key CLR (6); return to normal measured value by pressing and
holding down key CLR see 10.4.
7. Differential measurement (2490-2A only), plug 2 sensors of same type into
sockets M0 and M1 and then select measuring point M2; see 10.6
8. Evaluating a measuring operation
Call up maximum / minimum values by pressing keys MAX / MIN (6)
To delete max. / min. value(s) press and hold down key MAX or MIN ;
9. Programming or data output via interface (not type L)
Connect computer via interface cable to socket A1; see Manual 5.2.
Activate supplied software ALMEMO® Control.
Via ‘Setup interface’ set the COM port and transmission rate to 9600 bauds.
Program the sensors via ‘Program measuring point list’.
Measured value display and sensor adjustment via ´Measuring points - Meas-
ured values´
Data logging on the computer :
Program the cycle via ´Devices - Programming´
Open the terminal window via ´File - Terminal´
´File - Terminal - Open log ´, enter file name, ´Save´
Start the measuring operation by click ´Start´
Stop the measuring operation by click ´Stop´
´File - Terminal - Close log´
Activate file e.g. from MS-Excel and import using ´;´ as separator;

14
7. POWER SUPPLY
Power can be supplied to the measuring instrument in any of the following ways
: 3 AA alkaline batteries (included in delivery)
Mains adapter 12V, min. 1 A with ALMEMO® connector ZA1312-NAx
Electrically isolated power supply cable (12 VDC, 0.25 A) ZA2690-UK
12V DC clamp connector to socket DC ZA1000-FSV
Our product spectrum includes all the appropriate accessories.
7.1 Battery operation and
Power is supplied to the measuring instrument as delivered by 3 AA batteries.
At a current consumption of approx. 16 mA the operating time will be approx.
150 hours. The current operating voltage is displayed each time the the device
is switched on; this gives you a basis for estimating the remaining operating
time. When the remaining battery capacity drops to approx. 10 percent, the LO-
BAT arrow will appear in the display. If the batteries are completely discharged
the device will switch off. To replace old batteries first unscrew the battery com-
partment cover (7) on the rear of the device.
7.2 Mains operation
The ALMEMO® 2490A can be supplied with power from an external source pref-
erably using mains adapter ZA 1312-NAx (12 V / min. 1 A) via the DC socket (4).
Please ensure that the mains voltage is correct.
7.3 External DC voltage supply
The DC socket (4) can also be used to connect DC voltage, 12 V (minimum 200
mA). This is via an ALMEMO® connector (ZA1000-FSV). If, however, the power
supply has to be electrically isolated from the transducers, then is needed electri-
cally isolated supply cable ZA 2690-UK must be used. It will then be possible to
use the measuring instrument in a 12-volt or 24-volt on-board supply system.
7.4 Sensor supply
At the terminals + (plus) and – (minus) in the ALMEMO® connector there is a 9V
for battery operation and 12V for mains operation sensor supply voltage availa-
ble (maximum 400 mA) (self-healing fuse, 500 mA). Other voltages (12, 15, or
24 V or references for a potentiometer and strain gauge) can be obtained using
special connectors; (see Manual 4.2.5 and 4.2.6).
7.5 Switching ON / OFF,
To switch the device ON briefly press and release the key ON OFFr (6) in the
middle of the keypad; to switch the device OFF press and hold down the key ON
OFFr. After the device is switched off all saved values and settings are retained
intact; (see 7.6).
If interference (e.g. electrostatic) or a malfunction (e.g. battery failure) causes
the device to behave abnormally, the device can be reinitialized. To activate RE-
SET press and hold down the key CLR r when switching on. This will restore all
settings - except the device designation - to the factory default status. Only the
programming of the sensors in the ALMEMO® connectors remains unaffected.

7. Power supply
15
7.6 Data buffering
The sensor's programming is stored in the EEPROM on the sensor connector
and the device's calibration and programmed parameters are stored in the
EEPROM on the instrument itself, both on a fail-safe basis. Date and time-of-
day are retained intact if the device is just switched off but are lost when the
batteries are replaced.

16
8. CONNECTING THE TRANSDUCERS
Virtually any ALMEMO® sensor can be connected to ALMEMO® input socket
M0 (and / or M1 on version 2490-2) on the measuring instrument (1). To connect
your own existing sensors you simply need the appropriate ALMEMO® con-
nector.
8.1 Transducers
The ALMEMO® Manual includes detailed descriptions of the comprehensive
ALMEMO® range of sensors (see Manual Ch 3) and instructions for connecting
your own existing sensors to ALMEMO® instruments (see Manual Ch 4). All
standard sensors with an ALMEMO® connector usually have the measuring
range and units already programmed and can thus be connected to any input
socket without further adjustment. A mechanical coding system ensures that
sensors and output modules can only be connected to the correct sockets. All
ALMEMO® connectors incorporate two snap-lock levers; these snap into posi-
tion as soon as the connector is inserted into the socket, thus preventing unin-
tended disconnection if the cable is accidentally pulled. To withdraw the con-
nector, both these levers must be pressed in at the sides.
8.2 Measuring inputs and additional channels
The ALMEMO® 2490-1A has 1 input socket, version 2490-2A has 2 input sock-
ets (1); to these initially measuring channels M0 (and M1) are assigned. AL-
MEMO® sensors can, however, if necessary, provide up to 4 channels. The ad-
ditional channels can be used in particular for humidity sensors with 4 measur-
ing variables (temperature / humidity / dew point / mixture ratio) or for function
channels. Each sensor can if necessary be programmed with several measuring
ranges or scaling settings; and 2 or 3 sensors, if pin assignment so permits, can
be combined in a single connector (e.g. rH / NTC, mV / V, mA / V, etc.). The
additional measuring channel numbers per connector go up in steps of 10 (e.g.
the first sensor has channels M0, M10, M20, M30, the second sensor has chan-
nels M1, M11, M21, M31 etc.).
Device-internal channels (2490-2A only)
A further innovation on this device is its four additional device-internal channels.
The first of these M2 is programmed by default as differential channel M1 – M0.
This only applies, however, if there are two sensors with the same units and
same decimal point position connected at measuring points M0 and M1. How-
ever, all 4 channels can be programmed with any other function channels (e.g.
U-Bat, cold junction compensation, averages, etc.); (see Manual, Section 6.3.4).
The reference channels are by default Mb1 = M1 and Mb2 = M0.
The advantage of device-internal channels is that when using several sensors
for the same application these sensors do not have to be reprogrammed and
can be exchanged without losing the function channels. However, if the whole
application operates with just one sensor, then programming the function chan-
nels on the sensor itself makes more sense.

8. Connecting the transducers
17
On the measuring instrument this gives the following channel assignment :
8.3 Potential separation
When organizing a properly functioning measuring setup it is very important to
ensure that no equalizing current can flow between sensors, power supply, and
peripherals. All points must therefore lie at the same potential and / or any une-
qual potentials must be electrically isolated.
The 2 inputs on version 2490-2 are electrically isolated by means of photovoltaic
relays and a potential difference of maximum 50 VDC or 60 VAC is permissible
between them. Sensors combined within one connector and sensors with their
own power supply, however, are electrically interconnected and must therefore
be operated in isolation. The voltage at the measuring inputs themselves must
not exceed 5 volts (between B, C, D, A and - ).
The power supply is isolated by the mains adapter or by a DC/DC converter
(OA2490A-R02U or ZA2690-UK). Data and trigger cables are equipped with
optocouplers. If analog output cables are not electrically isolated the recording
device or the sensors must be zero-potential.

18
9. DISPLAY AND KEYPAD
9.1 Display
The display (5) on the ALMEMO® 2490A measuring instrument is a 2-row LCD
arrangement; the main field comprises 5x 7-segment digits (e) plus 2x 16-seg-
ment digits (d) for depicting the measured value;,the function field comprises
41/2x 7-segment digits (b) for depicting various measuring functions (a); there
are also 4 arrows (f) for depicting the operating status.
Function field
Main field
Display of measuring functions in the function field
Measuring point
Maximum value
Minimum value
Saved value
Memory capacity
Temperature value from double sensors
Configuration of device address
Configuration of analog reference channel
Configuration of locking
Configuration of automatic OFF
Special operating states and faults
Display segment test : runs automatically after switch ON
Supply voltage Display after segment test
Under 3.6 V : LOBAT arrow lights up.
Relative measuring with respect to a reference value : REL arrow lights up.
MAX 36.5
MIN 17.3
M 36.2
M O
26.5 °C
PO1
Adr
ACh1
Loc
AOFF

9. Display and keypad
19
Sensor correction or scaling : CORR arrow lights up.
Unlocked to enable sensor adjustment : FREE arrow lights up.
Checksum error in
device calibration :
Non-connected sensors,
deactivated measuring points :
Measuring range / function not permitted :
Sensor breakage : flashes
Outside of measuring range, undershoots
cold junction compensation flashes
or cold junction compensation breakage :
Overshoots values range (>65000) : flashes
Overshoots measuring range : Maximum value
flashes
Undershoots measuring range : Minimum value flashes
9.2 Keypad
To operate the device a keypad with 7 keys is provided :
Function : Key
To switch ON the device : (see Section 7.5) ON OFF
To switch OFF the device : ON OFF must be pressed and held down
Function : Key
Measuring points selection (see Section 10.1.1) M▲ or M▼
Displaying the maximum value : (see Section 10.2) MAX
To delete press and hold down
Displaying the minimum value : (see Section 10.2) MIN
To delete press and hold down
Zero-setting the measured value : (see Section 10.4) CLR
To delete press and hold down
Saving the measured value : (see Section 10.3) MEM
Displaying the battery voltage : ON OFF
CALEr
-----
Err
NiCr
CJ
65OOO

20
10. MEASURING OPERATIONS
With measuring instrument ALMEMO® 2490A all available measuring channels
are scanned by default semi-continuously; this permits continuous differential
measurements and ensures continuous temperature compensation for dynamic
pressure probes or chemical probes; (see Manual, Section 6.5.1.3).
Up to 4 or 12 measuring channels (type 2) can be displayed; see 8.2-
A measured value can be sent to an analog output; (see 11.2, Manual 5.1.1).
10.1 Measured value
After switching ON first of all a segment test is
performed; then the battery voltage appears
and if the batteries are almost empty (<3.6 V)
the LOBAT arrow also appears.
The measured value is then displayed with the
appropriate units in the main field and the meas-
uring point is displayed in the function field. All
special operating states possible for the meas-
ured value are explained in Section 9.1.
10.1.1 Selecting a measuring
point
By pressing key M▲ you can select one after the other all active measuring
points and have the current measured value displayed for each. By pressing
key M▼ you can return to the previous channel.
To increment the measuring channel press key : M▲
To decrement the measuring channel press : M▼
When switching between channels the abbreviation for the measuring range is
briefly displayed; (see 10.1.2).
10.1.2 Measuring ranges
With each channel switchover or sensor breakage the abbreviation for the
measuring range appears in the display. For identification purposes the follow-
ing table lists all possible measuring ranges.
Transducers
Sensor / con-
nector
Measuring range
Units
Abbre-
viation
Pt100-1
FP Axxx
-200.0... +850.0
°C
P104
Pt100-2
FP Axxx
-200.00...+400.00
°C
P204
Ni100
ZA 9030-FS3
-60.0... +240.0
°C
N104
NiCr-Ni (K)
FT Axxx
-200.0...+1370.0
°C
NiCr
NiCroSil-NiSil (N)
ZA 9020-FSN
-200.0...+1300.0
°C
NiSi