The dataTaker range of data loggers have 2 different types of analog input channel multiplexers, solid state (CMOS) multiplexer or relay multiplexer.

The models of the dataTaker data loggers which have each of these multiplexer types are as follows

Solid State (CMOS) Multiplexer
   - dataTaker 50, 500 and600

Relay Multiplexer
   - dataTaker 505, 605, 515 and615
   - Channel Expansion Module (CEM-AD)

Throughout this section reference will be made to solid state or relay multiplexing, rather than to individual dataTaker models. Confirm from the above list which dataTaker model you are using.

The dataTaker 50 has 5 analog input channels, which can be used for measuring up to 5 analog input signals as differential inputs, or up to 10 analog input signals single ended inputs.

The 5 analog input channels of the dataTaker 50 provide for channel capacities as follows

15 single ended channels for current, current loop and AD590/AD592
temperature sensors

10 single ended channels for all other analog signal types

10 single ended channels for resistance and RTDs

The dataTaker 500/600 series loggers and the Channel Expansion Module (CEM-AD) have 10 analog input channels, which can be used for measuring up to 10 analog input signals as differential inputs, or up to 30 analog input signals single ended inputs.

The 10 analog input channels of the dataTaker 500/600 series loggers and the Channel Expansion Module (CEM-AD) provide for channel capacities as follows

40 single ended channels for current, current loop and AD590/AD592
temperature sensors

30 single ended channels for all other analog signal types.

20 single ended channels for resistance and RTDs

The analog input channels of the dataTaker and Channel Expansion Module (CEM-AD) can be used in any mix of differential and single ended channels.

The use of the analog input channels as differential or single ended channels for measuring analog signals is specified as part of the channel specification in the channel list of the Schedule (see Section III ñ Specifying Channels).

The Analog Input Channels

The analog input channels of the dataTaker and Channel Expansion Module (CEM-AD) comprise four terminals

the positive (+) input terminal

the negative (ñ) input terminal

the Excite (T) terminal

the Analog Return (R) terminal

The screw terminal connections are identical for all analog channels, and are laid out as illustrated below

 

 

Figure 27 ñ Analog Input Channel Terminal Layout

 

The dataTaker fundamentally measures the voltage of input signals applied to the analog input channels.

The input channels are configured in various ways to enable measurement of current, resistance, frequency and period signals.

Voltage Ranges ñ Solid State Multiplexer

The three voltage ranges for the dataTaker 50, the dataTaker 500 and the dataTaker 600 models which have the solid state (CMOS) multiplexer are

±25.000 mV

±250.00 mV

±2500.0 mV

The analog to digital converter autoranges between these input ranges, with range changing occurring at approximately 120% and 15% of nominal full scale for each range. The highest range allows up to 30% over-range, which allows voltages in the range of approximately ±3250 mV to be measured.

An out of range input signal results in data of ±99999.9 units. An out of range input is also indicated by the error message ëE11-input(s) out of rangeí.

The operation of the analog to digital converter is discussed in detail in Section II ñ Analog Processing.

Voltage Ranges ñ Relay Multiplexer

The voltage ranges for the dataTaker 505, the dataTaker 515, the dataTaker 605 and the dataTaker 615 models which have the relay multiplexer depend on the internal attenuator.

If the internal attenuator is not selected, then the three low voltage ranges are

±25.000 mV

±250.00 mV

±2500.0 mV

If the internal attenuator is selected, then the three high voltage ranges are

±7 Volts

±70 Volts

±100 Volts

The analog to digital converter autoranges between these input ranges, with range changing occurring at approximately 120% and 15% of the nominal full scale for each range. The highest range allows up to 30% over-ranging, allowing voltages in the range of approximately ±3250 mV to be measured in the low voltage range, and ±130 Volts to be measured in the high voltage range.

An out of range input signal results in data of ±99999.9 units. An out of range input is also indicated by the error message ëE11-input(s) out of rangeí.

The operation of the analog to digital converter is discussed in detail in Section II ñ Analog Processing.

Termination of Analog Inputs

The analog input channels of the dataTaker have an input impedance of >100 MOhm. However the analog input channels can be internally tied to the logger ground or ëterminatedí via 1 MOhm resistors. These terminating resistors prevent ungrounded input signals 'floating' out of the common mode range of the dataTaker, particularly for the solid state multiplexed models.

This input termination is the default configuration for most of the differential signal types, such as low level voltage, frequency, period, thermocouple and analog state.

The input termination can be enabled or disabled by channel options, which are declared as part of the input signal identification (See Section III ñ Channel Options).

In DeTransfer, input termination is selected by the channel option T for example

In this case a differential voltage applied to analog channel 8 is to be measured with the inputs terminated to the dataTaker ground via the 1 MOhm resistors. This is the default configuration for most differential voltage and thermocouple signal types, and normally does not need to be specified.

The input termination resistors can be disabled if required, for example if differentially connected thermocouples are externally grounded, or if a sensor such as a glass electrode for pH or specific ion measurement has a high output impedance and cannot match the 1 MOhm input impedance of the terminated inputs. Input termination can be disabled by the Unterminate channel option as follows

In this case the type T thermocouple connected to analog input channel 6 is to be measured Unterminated. The 1 MOhm resistors are disconnected from the inputs during measurement of the input signal. Note that input termination defaults to terminated for differential thermocouples.

The internal termination 1 MOhm resistors are managed in the DeLogger Program Builder by selecting Channel Options:TerminationÖ for the channel, which opens the Termination dialog box as follows

 

 

Differential Analog Input Mode

The differential analog input mode can be used to measure the fundamental signal types of voltage, current, resistance and frequency, and for sensors providing these signals.

In the differential mode, the analog signal is applied between the +ve and ñve terminals of the analog input channel, as illustrated in Figure 28 below

 

 

Figure 28 ñ Differential Analog Input

 

The unknown voltage V is measured between the +ve and the ñve terminals.

However this is a somewhat simplistic situation which implies that there are no common mode voltages or noise voltages in the measurement system.

Figure 29 below illustrates a more realistic situation, where there are common mode or noise voltages composed of DC offset voltages, ground potential differences and electrical noise voltages which can effect the measurement accuracy.

 

 

Figure 29 ñ Differential Analog Input With Common Mode Voltages

 

The unknown voltage V is measured between the +ve and the ñve terminals. Any common mode voltage or NOISE voltage which is in the common mode range of the dataTaker is rejected.

The +ve and the ñve signal lines may float within the dataTaker common mode input voltage limits of

solid sate (CMOS) multiplexer
   ñ3.5 Volts to +3.5 Volts with respect to ground

relay multiplexer
   ñ100 Volts to +100 Volts with respect to ground
     when the internal attenuators are selected

The voltage inputs are internally tied to ground or terminated via the 1 MOhm resistors, to prevent ungrounded signals 'floating' out of the common mode range.

Differential analog input channels are sampled and the data is returned when Schedules execute or run.

Using DeTransfer, the command for example

Instructs the dataTaker to measure the differential voltages applied to analog input channel 1 and to channels 5 through 10 inclusive. The V indicates that the signal applied to these channels is to be measured as a voltage.

Instructs a dataTaker505 or 605 to measure the differential high level voltages applied to analog input channel 2 and to channels 4, 5 and 6. The HV indicates that the signal applied to these channels is to be measured as a voltage in the high range.

Using DeLogger, differential analog channels are selected from the Voltage Wiring Configurations dialog that opens when you select the analog input channel as follows

 

 

Single Ended Analog Input Mode

In the single ended input modes the positive terminal, negative terminal and Excite terminal (dataTaker 500/600 series loggers and the Channel Expansion Module only) of the analog input channels are used as separate input channels as follows

Positive single ended channel, where the positive line of the signal is connected to the +ve terminal of the analog channel, and the negative line of the signal is connected to a common reference.

Negative single ended channel, where the positive line of the signal is connected to the ñve terminal of the analog channel, and the negative line of the signal is connected to a common reference.

Excite single ended channel, where the positive line of the signal is connected to the Tterminal of the analog channel, and the negative line of the signal is connected to a common reference. This mode is supported in the dataTaker 500/600 series loggers and the Channel Expansion Module (CEM-AD) only, and is not supported in the dataTaker 50.

The negative inputs of the analog channels are non-inverting such that when a positive signal is applied to the negative terminal of a channel, positive data is returned.

The single ended analog inputs can be referenced in two ways as follows

internally referenced single ended inputs, where the input signal is referenced to the Analog Return (R) terminal of each channel.

externally referenced single ended inputs, where the input signal is referenced to a common external point which is connected to the single ended external reference terminal SE REF.

Although these input modes are referred to as the single ended input modes, the signals are actually measured differentially between the indicated terminal of the analog input channel and the indicated reference.

The single ended analog input modes can be used to measure fundamental voltage, current, resistance, frequency and period signals, and sensors providing these signals.

The main advantage of single ended input modes is that the number of measuring channels is increased. However there may be some decrease in accuracy due to noise.

Note :  The Excite terminal single ended input is not supported in the dataTaker 50. All references to Excite terminal single ended input (T) modes throughout this manual only apply to the dataTaker 500 /600 series loggers, and to the Channel Expansion Module (CEM-AD).

Single Ended Inputs Referenced to Analog Return

Single ended analog inputs referenced to Analog Return may be used for measuring voltage, current, frequency and period. Resistance cannot be measured in this mode.

Analog signals are connected for single ended measurement between any of the positive (+) terminal, the negative (ñ) terminal or the Excite (T) terminal of the analog channel, and the Analog Return (R) terminal of the same channel.

The connection of single ended inputs referenced to Analog Return is illustrated below

 

 

Figure 30 ñ Positive Terminal Single Ended Input Referenced to Analog Return

 

The unknown voltage V is measured between the +ve and Analog Return terminals.

However this is a somewhat simplistic situation which implies that there are no common mode voltages or noise voltages in the measurement system.

The input signals connected to the +ve, ñve and T terminals of the dataTaker must remain within the common mode limits with respect to the logger ground.

A more realistic situation is shown in Figure 31 below, where the input signal contains common mode or noise voltages composed of DC offset voltages, ground potential differences and electrical noise voltages. These common mode voltages can effect the measurement accuracy.

The single ended input modes are prone to errors due to ground loop noise. Further, excessive ground current into the Analog Return terminal may damage the analog input circuitry. This is due to ground loop currents (which can be large) causing a voltage drop along the return wire.

These problems are largely overcome by not grounding sensors externally, or by externally referencing the single ended inputs (see below).

 

 

Figure 31 ñ Positive Terminal Single Ended Input With Common Mode Voltages,
Referenced to Analog Return

Single ended inputs referenced to Analog Return are sampled and the data is returned when Schedules execute or run.

Using DeTransfer, single ended inputs referenced to Analog Return are read by the command for example

which instructs the dataTaker to measure the single ended voltages applied between

the T Excite terminal and the Analog Return terminal of analog input channel 1, which is identified as channel 1T (supported by dataTaker 500/600 series loggers only)

the +ve terminal and the Analog Return terminal of analog input channel 1, which is identified as channel 1+

the -ve terminal and the Analog Return terminal of analog input channel 1, which is identified as channel 1ñ

The V indicates that the signal applied to these channels is to be measured as a voltage.

Using DeLogger, single ended analog channels referenced to Analog Return are selected from the Voltage Wiring Configurations dialog that opens when you have selected the analog input channel as follows

 

 

Note : These examples also illustrate that an analog input channel of the dataTaker 500/600 series loggers and Channel Expansion Module (CEM-AD) can be used to measure three different voltages, and that an analog channel of the dataTaker 50 can be used to measure two different voltages.

Single Ended Inputs Referenced to an External Common

Single ended analog inputs can be measured with reference to an external reference or 'common'. This mode can be used for measuring voltage, current, current loop, frequency and period. Resistance cannot be measured by this input mode. External references can be used for single ended analog inputs whenever a common reference point can be established in a sensor system remote from the dataTaker.

The analog input signal is applied between any of the +ve, ñve or T terminal of the analog input channel, and the established external reference point. The external reference is connected to the single ended external reference input terminal SE REF.

The single ended reference input terminal SE REF has a high input impedance, resulting in very small ground currents. The connection of single ended inputs referenced to an external common is illustrated in Figure 32 below

 

 

Figure 32 ñ Single Ended Analog Inputs Referenced to an External Common

 

The unknown voltages V are measured between the +ve and ñve input terminals respectively, and the SE REF input terminal.

In this configuration, the common mode voltages and the noise voltages occurring between the external common point and the dataTaker are rejected.

Single ended measurements which are to be referenced to an external common applied to the SE REF input terminal are specified by the X channel option.

Single ended inputs referenced to an external common connected to SE REF, are sampled and data is returned when Schedules execute or run.

Using DeTransfer, single ended measurements that are to be referenced to an external common connected to SE REF are measured by the command for example

which instructs the dataTaker to measure single ended voltages between

the T Excite terminal of analog input channel 1 (channel 1T) and an external reference input to SE REF

the +ve terminal of analog input channel 5 (channel 5+) and an external reference input to SE REF

the ñve terminal of analog input channel 6 (channel 6ñ) and an external reference input to SE REF

The V indicates that the signal applied to these channels is to be measured as a voltage. The X channel type option indicates that the single ended voltage is measured between the input terminal of the channel and SE REF.

Using DeLogger, single ended analog channels referenced to SE REF are selected from the Voltage Wiring Configurations dialog that opens when you have selected the analog input channel as follows

 

 

Using Externally Referenced Single Ended Inputs to Reduce Cabling

Externally referenced single ended analog inputs can also be used where a number of differential voltages must be measured at some distance from the dataTaker.

Figure 33 illustrates cabling required to connect the two differential voltages directly to the dataTaker analog input channels, requiring four conductors and two channels.

Figure 34 illustrates the same two sensors connected as single ended inputs referenced to an external common point, requiring only three conductors and one channel.

 

 

Figure 33 ñ Measurement of Remote Differential Voltages

 

 

Figure 34 ñ Measurement of Remote Differential Voltages

 

The negative outputs of the remote sensors are connected to an external common point adjacent to the sensors, which in turn is connected to the SE REF input terminal. The positive outputs from each sensor are connected to the analog input terminals. The number of cables needed to connect sensors to the dataTaker is reduced, and half of the number of analog input channels are used.