dataTaker - Data Loggers, Powerful and Flexible Data Acquisition & Data Logging Systems

The Channel Expansion Module

The dataTaker 500/600 series loggers can be expanded by connecting 1 or 2 Channel Expansion Modules (CEM-AD) in a daisy chain configuration.

The Channel Expansion Module (CEM-AD) has a channel capacity as follows

10 analog input channels, implemented as 10 differential or 30 single ended
channels which can be used in any mix

20 digital input channels, implemented as TTL/CMOS/Voltage free contact
compatible channels

10 digital output channels, implemented as 5 contact closure outputs and
5 open collector outputs

Installing the Channel Expansion Module

One or two Channel Expansion Modules (CEM-AD) can be connected to a dataTaker 500/600 series logger. The connection between the dataTaker 500/600 series loggers and the Channel Expansion Modules is via 25 pin connectors located at one end of the logger, and at each end of the Channel Expansion Modules.

The data logger and the modules are interconnected by 25 core cable. Each cable must not exceed 50 cm (20 ins) in length, and the total length of cables including the length of the logger and modules must not exceed 2 metres (6 feet).

Note: The Channel Expansion Modules must not be connected to the dataTaker while the logger is powered.

Disconnect external power and all batteries from the dataTaker before connecting the Channel Expansion Module to the logger. The Channel Expansion Module is designed as a permanent fixture for the dataTaker, and must not be disconnected until power and all batteries are disconnected.

The Channel Expansion Module is powered by the dataTaker, and does not require a separate power supply.

The footprint size of the Channel Expansion Module is identical to that of the dataTaker, and is compatible with the range of dataTaker enclosures as follows

Large Industrial Enclosure - accommodates one dataTaker and one Channel Expansion Module (CEM-AD)

Small Industrial Cabinet - accommodates one dataTaker and two Channel Expansion Modules (CEM-AD)

The dataTaker and Channel Expansion Module(s) can also be fitted into any suitably sized enclosure, either side by side or end to end depending on the shape and size of the enclosure.

When using thermocouples with the dataTaker and the Channel Expansion Modules, it is recommended that the dataTaker and Channel Expansion Modules be fitted into a suitable metal enclosure to avoid thermal gradients across the modules. A metal enclosure also protects against magnetic and electrical interference on the modules and interconnecting cables.

Channel Expansion Module Number

The Channel Expansion Modules (CEM-AD) do not have a hardware address. Once the interconnecting cable is fitted and the dataTaker is powered up, each Channel Expansion Module available is identified and numbered in software as module 1 and module 2.

The Channel Expansion Module connected to the dataTaker becomes module number 1, and the next Channel Expansion Module becomes module number 2.

To confirm the connection of a Channel Expansion Module to the dataTaker, enter the TEST command from DeTransfer as follows


The TEST command will return a report as follows

dataTaker 526  Ver 7.00
Vos (mV)            0.117
Vfo  (V)            7.873
Fc (kHz)            17.784
CMRR(db)            101.2
Vos3(mV)            0.322
Tos                 1.0022
Ios (nA)            -3
Ibia(nA)            13
Ibat(mA)            -100.0
Vbat (V)            6.3
Vos*(uV)            -95
Vos+(uV)            33
Vos-(uV)            10
VosR(uV)            66
Vosd(uV)            5
Ics1(mA)            2.5011
Ics2(uA)            249.93

Using DeLogger, the TEST command is run by clicking on the TEST button on the main toolbar of DeLogger, or by selecting ResetÖ under the dataTaker menu..



The first line of the TEST report contains information about the configuration of the dataTaker (See Section III ñ TEST Command) and version of firmware.

The digit 6 is appended to the dataTaker xxx for each Channel Expansion Module that is connected to the logger.

Connection of the Channel Expansion Module(s) to the dataTaker 500/600 series loggers is illustrated below.



Figure 125 - Channel Expansion Module Connection

Commanding the Channel Expansion Module 

The Channel Expansion Module (CEM-AD) provides increased channel capacity for the dataTaker 500/600 series loggers. In general the channel and signal measurement specifications of the Channel Expansion Module (CEM-AD) are the same as the dataTaker model to which it is connected.

These channels and signal types are commanded in the same manner as for the dataTaker to which the Channel Expansion Module(s) are connected.

The Channel Expansion Module has a relay multiplexer for the analog input channels, similar to that for the dataTaker 505,515, 605 and 615.

If the Channel Expansion Module is connected to a dataTaker 500 or dataTaker 600 data logger, then the module has a maximum input voltage of ±2500 mV and a common mode range of ±3.5 Volts.

If the Channel Expansion Module is connected to a dataTaker 505, dataTaker 515, dataTaker 605, dataTaker 615 data logger, then the module has a maximum input voltage of ±100 Volts and a common mode range of ±100 Volts.

The Channel Expansion Module is capable of withstanding in excess of 500 Volts for 50 mS, or 100 Volts continuously, on any unselected analog input channel.

Module Number

The commands used to specify channels of the Channel Expansion Module (CEM-AD), and channel options for channel configuration, follow the same conventions as those used for the dataTaker.

However each command directed to a Channel Expansion Module is prefixed by a module number and a colon character as follows

n:channel type(channel options)


n:       the CEM number, either 1 or 2.

Using DeTransfer, channels on a Channel Expansion Module are specified as follows

1:6TK  2:1..3DS

which specifies

a K type thermocouple connected to analog channel 6 of CEM number 1

digital state channels 1 through 3 of CEM number 2

Using DeLogger,



channels on the CEM-AD are selected in the Program Builder as part of a program as follows

Analog Channels:

firstly select any analog channel of the logger, say analog channel 10, and attach the sensor type that is connected to the target channel on the CEM

then reassign this channel to the CEM by right clicking on the new ëpseudoí channel icon, and select Channel Options:Channel Number:CEMn:channel number

Digital Channels:

firstly select any digital channel of the logger, say digital channel 1, and select the state or counter input type that is connected to the target channel on the CEM

then reassign this channel to the CEM by right clicking on the new ëpseudoí channel icon, and select Channel Options:Channel Number:CEMn:channel number

The raw data returned for channels of the Channel Expansion Module have the module number prefixed to the channel identification as follows

1:6TK  156.65 Deg C
2:1DS  1 State
2:2DS  0 State
2:3DS  1 State

Internal Channels 

The Channel Expansion Module (CEM-AD) has two internal channels, which are used as reference channels when monitoring thermocouples.

The two internal channels are the module temperature which is sensed by a LM35 monolithic temperature sensor, and an electrical zero channel.

These internal channels are identified in the general format as follows

n:1%LM35           internal temperature channel

n:2%V                electrical zero channel

where n is the module number.

Over Voltage Protection

The Channel Expansion Module (CEM-AD) does not include built in energy absorbing lightning protection.

However all analog input channel terminals except for the Analog Return terminals are capable of withstanding 1.5KV for 10µS, 500V for 50mS and 100V indefinitely. The Analog Return terminal can withstand only 5% of these voltages.

The above withstanding voltages apply only to unselected channels. While a channel is selected for reading (a process that typically takes 30mS), these withstanding voltages are reduced to the common mode voltage range of the dataTaker as follows

dataTaker 500 and 600                             ±5 Volts relative to ground

dataTaker 505, 515, 605 and 615   ±100 Volts relative to ground

In applications where scanning is infrequent (say not more than every 3 hours), the probability of a scan being co-incident with a lightning strike is very low.

Where lightning is frequent, it is strongly recommended that external energy absorbing lightning protection be wired to each sensor line. Further, it is recommended that the dataTaker 505, 605, 515 or 615 loggers which have higher withstanding voltages be used.

Using Thermocouples 

The Channel Expansion Module (CEM-AD) fully supports thermocouples for cold junction compensation and zero voltage compensation.

The Channel Expansion Module has a LM35 temperature sensor located so that it senses the temperature of the analog input channel screw terminals. These terminals are the thermocouples reference junction.

The dataTaker will automatically measure the Channel Expansion Module temperature and electrical zero when scanning a thermocouple channel on the module. These values are then used for reference junction compensation.

The accuracy of thermocouple measurement is dependent on the isothermal condition of the reference junction. If a temperature gradient develops between the modules temperature sensor and the input terminals, the error will approximately equal the temperature difference.

The module utilises relays for channel selection and digital output. These are a source of heat and each relay dissipates 150mW when switched on. For maximum thermocouple accuracy, ensure that these relays are not left on unnecessarily.

A not so obvious reason that a relay may be left on is that the last channel in a scan remains selected if Parameter15 is set to 1 or 2. This can be resolved if P15 is set to zero, or a dummy channel is placed at the end of the Schedule. A good choice would be 1%V(M18:156,W).

Power Consumption 

The Channel Expansion Module (CEM-AD) consumes very little power if the dataTaker to which it is attached is allowed to sleep.

While scanning channels on the Channel Expansion Module, the current drawn from the dataTaker will increase to approximately 60mA. Additional current is required if the digital output relays are switched on. Each of the five relays will draw 35mA, however these relays are automatically switched off when the dataTaker sleeps.

A summary of current draw is tabulated below:



Current Draw


Awake, no scanning or digital I/O

Digital inputs grounded

Scanning CEM channels

All relay outputs ON (1..5DSO=1)

Worst case condition








External Excitation 

The Channel Expansion Module (CEM-AD) can power or excite sensors from the Excite (]) terminal of the analog channels. Excitation can be provided either by the standard current and voltage sources, or by an external power source.

For sensors that require non-standard powering or excitation, an External Excitation input terminal is able to direct power to the Excite (]) terminal of selected analog channels.

This option must be enabled by moving a jumper to the outer two pins on a three pin header. For location details of the jumper See Section I - Construction of the Channel Expansion Module.

The normal position of the jumper (between the inner two pins) provides the standard dataTaker 250.0 µA, 2.500 mA or 4.5V excitation.

If the external excitation option is selected these standard excitations are not available on any channel of module. Care must be taken in assigning channels. If for example an Expansion Module is wired with a four wire RTD, and several bridges requiring 12 Volt excitation, then the 12 Volt would be applied to the RTD when it is scanned. The RTD would probably be damaged.

Page Content


Title and Waranty

Go to: Section 2 | Section 3

Section 1

Construction of the dataTaker 50

Construction of the dataTaker 500 600

Construction of the CEM

Getting Started


Section 2


Powering the dataTaker

Powering Sensors from the dataTaker

The Serial Interfaces

The RS232 COMMS Serial Interface

The NETWORK Interface

Analog Process

Connect Analog

Analog Chns

Measuring Low Level Voltages

Measuring High Level Voltages

Measuring Currents

Measuring 4-20mA Current Loops

Measuring Resistance

Measuring Frequency and Period

Measuring Analog Logic State

Measuring Temperature

Measuring Temperature with Thermocouples

Measuring Temperature with RTDs

Measuring Temperature with IC Temperature Sensors

Measuring Temperature with Thermistors

Measuring Bridges and Strain Gauges

Measuring Vibrating Wire Strain Gauges

The Digital Input Channels

Monitoring Digital State

The Low Speed Counters

The Phase Encoder Counter

The High Speed Counters

The Digital Output Channels

The Channel Expansion Module

Installing The Panel Mount Display


Section 3

Programming the dataTaker

Communication Protocols and Commands

Entering Commands and Programs

Format of Returned Data

Specifying Channels

The Analog Input Channels

The Digital Input Channels

The Counter Channels

The Digital Output Channels

The Real Time Clock

The Internal Channels

Channel Options



Scaling Data - Polynomials, Spans and Functions

CVs Calcs and Histogram

Logging Data to Memory

Programming from Memory Cards


Switches and Parameters


Writing Programs

Keypad and Display

Error Mess Text

Appendix A - ASCII

Appendix B - ADC Timing