This section describes the measurement of high level differential (double ended) DC voltages and single ended DC voltages with the dataTaker.

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, 500 and 600 data loggers have the solid state multiplexer, and have a maximum voltage measurement range of ñ2500 mV to +2500 mV. However these dataTakers can also measure high level voltages by externally attenuating the signal with attenuation resistors.

The dataTaker 505, 515, 605 and 615 data loggers have the relay multiplexer, and also have precision internal attenuation resistors as standard. These dataTakers have a maximum input measurement range of ñ100 Volt to +100 Volt, when the internal attenuators are selected via command. External attenuation of high level voltages is not normally required with these dataTaker models.

Note :  The Channel Expansion Module (CEM-AD) does not have internal attenuation resistors, and the maximum voltage range of the modules is determined by the maximum voltage range of the dataTaker to which it is connected.

The dataTaker 50 has 5 differential analog input channels, which may also be used as 10 single ended input channels. The dataTaker 500/600 series loggers and Channel Expansion Module (CEM-AD) have 10 differential analog input channels, which may also be used as 30 single ended input channels. Any combination of differential and single ended analog input channels can be used for measuring high level voltages.

External Attenuation of High Level Voltages

High level voltages outside the range of –2500 mV to +2500 mV can be measured by externally attenuating the signal into this range, and applying the attenuated voltage to the analog input channels as a low level voltage. This applies to all dataTaker models which have solid state multiplexers, but can also be used for dataTaker models which have the relay multiplexer.

Externally attenuated high level voltage can be measured in several ways as follows

attenuated differential inputs on any of the analog input channels

attenuated single ended inputs referenced to Analog Return

attenuated single ended inputs referenced to an external common

The attenuated voltage input capability of the dataTaker in effect provides additional user definable voltage measurement ranges.

The attenuated voltage can be re-scaled after measurement to the magnitude of the original voltage by using

a channel factor, which represents the attenuation factor

a Polynomial or Span (See Section III ñ Scaling Data, Polynomials, Spans and Functions) which represents the attenuation factor. Polynomials and Spans also allow an offset to be applied to the measured voltage, and allow data to be re-scaled to other units.

Attenuation of voltage inputs also has the additional benefits of providing a greater level of input protection, and of reducing any problem common mode voltages since these are attenuated in the same proportion as the signal voltages.

External Voltage Attenuator Networks

Voltage attenuator networks are simple resistor pairs, which reduce the high level voltage signal to ±2500 mV (or ±3250 mV including the allowable over-ranging) to suit the voltage input range of the dataTaker data loggers.

A typical voltage attenuator network is illustrated in Figure 39.

 

 

Figure 39 ñ Schematic of a Voltage Attenuator Network

 

The voltage reduction by the network is described as the voltage attenuation factor, which is calculated by the relationship

Voltage Attenuation Factor = (R₁ + R₂)/R₂

and is declared to the dataTaker as a scale factor in the channel options for the input channel in schedule lists (see below).

The voltage attenuation factor can be a floating point decimal value, and is used to directly re-scale the measured low level voltage from the voltage attenuator network to the magnitude of the original high level voltage.

The table below provides suitable preferred resistor values for commonly used attenuation ratios

 

Attenuation Factor	R1	R2
5.5:1	10 KOhm	2.2 KOhm
	100 KOhm	22 KOhm
11:1	10 KOhm	1 KOhm
	100 KOhm	10 KOhm
48:1	470 KOhm	10 KOhm
101:1	1 MOhm	10 KOhm

 

The attenuation ratios in the table above are not exactly 5:1, 10:1, 50:1, 100:1 etc. because this would require non-standard resistors. The resistors used above are standard or preferred magnitudes, which are commonly available.

When building attenuators, the accuracy of voltage measurement will be directly determined by the accuracy and temperature tolerance of the resistors. Where possible use precision 0.1% resistors.

Power rating of the attenuator resistors is not critical, since signals should only be a few milliamps. Generally, 0.5 Watt resistors will be suitable.

Installing Voltage Attenuator Networks

When high level voltages outside the voltage measuring range of the dataTaker are to be measured, the voltage signal can be externally attenuated by resistor networks installed in one of the following ways

by installing  the voltage attenuator networks directly onto the screw terminals of the analog input channels

by installing the voltage attenuator networks remotely from the dataTaker, possibly at the source of the high level voltages

An external voltage attenuator network can be installed as follows

 

 

Figure 40 ñ Installing a Voltage Attenuator Network

 

Small resistor mounting pads are available from your dataTaker supplier. Attenuation resistors can be soldered onto the pad. The pad is directly connected into the screw terminals of input channels, and signal leads connect to the rear edge of the pad.

Differential Measurement of Externally Attenuated Voltage

Whenever externally attenuated high level voltages are measured as differential inputs, then both of the signal lines from the high level voltage signal must be attenuated by separate resistor networks. Each side of the high level voltage is connected via a separate voltage attenuator to the +ve and ñve terminals of an analog input channel.

The differential voltage measured by the dataTaker is the difference of the voltages between the +ve and ñve terminal. For a discussion of when to use differential mode see Section II ñ Measuring Low Level Voltages.

Common Mode Voltage Limits

When using external voltage attenuator networks to attenuate high level voltage signals, then any common mode voltages present in the signal are also attenuated by the voltage attenuator networks.

The maximum allowable common mode voltage for the high level voltage inputs is ±(attenuation factor x 3.5) Volts.

Note :  The characteristic of attenuator networks also attenuating the common mode voltages allows low level voltages with high common mode or offset voltages to be measured.

The common mode voltage range of the dataTaker can be reduced by attached voltage attenuation networks, if the two attenuation networks of a differential input are not closely matched.

For example if an attenuation ratio of 10:1 is required, which is built from a 100 KOhm and a 10 KOhm resistor for the +ve input, and a 10 KOhm and 1 KOhm resistor for the ñve input, then the common mode voltage range will not be the same for both inputs and the lesser will prevail.

Differential Measurement

When high level voltages are connected to the dataTaker for differential measurement, both of the signal lines of the high level voltage must be externally attenuated by separate resistor networks.

High level voltages are connected to the analog input channels as differential inputs as follows

 

 

Figure 41 ñ Connecting Externally Attenuated High Level Voltages
as Differential Inputs

 

Note :  Both resistor networks must be of the same attenuation factor. The differential voltage measurement is made between the +ve and ñve terminals of the analog input channel.

High level voltages connected to the dataTaker as externally attenuated differential inputs are read when a Schedule containing the channel is executed.

The attenuation factor for the voltage attenuator networks is specified as a scale factor in the channel options for the input channel, and is used by the dataTaker to re-scale the measured voltage.

Using DeTransfer, externally attenuated high level voltages are measured differentially by the command for example

which instructs the dataTaker to measure these inputs on analog input channels 1 and 5.

The voltage measured by channel 1 is attenuated by a 10:1 resistor network, and so the data is multiplied by 10.0 before being returned. The voltage measured by channel 5 is attenuated by a 25.2:1 resistor network, and the data is multiplied by 25.2 before being returned.

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

The U channel option disconnects or Unterminates the internal 1 MOhm input termination resistors during measurement of the voltage. If the termination resistors are not disconnected, then these will influence the attenuation factor of the external resistor network.

The data is returned in units of mV.

Using DeLogger, externally attenuated high level voltages can be measured by the following Program Builder program. The differential connections are selected from the Voltage Wiring Configurations dialog which opens when you have selected the analog input channel, and the attenuation factor is specified via the Attenuation button.

 

 

The dataTaker will read the inputs every 5 minutes, and readings are stopped by entering a H (Halt) command.

Alternatively the data could be scaled using a Polynomial, and assigned an appropriate engineering unit (See Section III ñ Scaling Data, Polynomials, Spans and Functions).

Using DeTransfer, this can be done by the commands for example

An offset can also be applied to the readings if required, by assigning a value to the first coefficient of the Polynomial.

Using DeLogger, the Polynomials must be defined in the Program Builder under the Settings:Polynomials tab, and attached to the voltage measuring channels as follows

 

Declare a Polynomial for the attenuator scaling

Attach the Polynomial to the channel

 

Single Ended Measurement of Attenuated Voltage

Externally attenuated high level voltages can be measured as single ended inputs as follows

as attenuated single ended input to the +ve, ñve or T input terminal, which is referenced to Analog Return

as attenuated single ended input to the +ve, ñve or T input terminal, which is referenced to an external common connected to the SE REF terminal

When high level voltages are measured as single ended inputs, only the positive or non-grounded line of the high level voltage signal is attenuated.

The dataTaker treats the voltage signal applied to the +ve, ñve or T input terminal of the analog channel as the active input, and measures this with respect to Analog Return or SE REF.

The dataTaker 50 does not support single ended voltage measurement for the Excite (T) terminal.

For a discussion of when to use single ended input modes see Section II ñ Measuring Low Level Voltages.

Single Ended Measurement Referenced to Analog Return

Whenever high level voltages are connected to the dataTaker for measurement as single ended inputs, the positive signal of the high level voltage must be externally attenuated by a resistor network.

High level voltages are connected to the analog input channels as single ended inputs referenced to Analog Return as follows

 

 

Figure 42 ñ Connecting Attenuated High Level Voltages as Single Ended Inputs
Referenced to Analog Return

 

The attenuated single ended voltage is measured between the +ve, ñve or T terminal and Analog Return. The dataTaker will measure the polarity of the input voltage.

Externally attenuated high level voltages connected to the analog input channels as single ended inputs referenced to Analog Return are sampled and data returned when a Schedule containing the channel is executed. The attenuation factor is specified as a scale factor in the channel options for the input channel, and is used to re-scale the measured voltage.

Using DeTransfer, externally attenuated voltages connected as single ended inputs referenced to Analog Return are measured by the command for example

which instructs the dataTaker to measure inputs on analog channel 1+ and channel 5ñ. The voltage measured on channel 1+ is attenuated by 5.5:1, and is multiplied by 5.5. The voltage measured on channel 5ñ is attenuated by a 10:1, and is multiplied by 10.0.

Using DeLogger,

 

externally attenuated high level voltages connected as single ended inputs referenced to Analog Return can be measured by the program above.

The single ended connections are selected from the Voltage Wiring Configurations dialog which opens when you have selected the analog input channel, and the attenuation factor is specified via the Attenuation button.

The internal 1 MOhm input termination resistors are not selected during single ended measurement of voltages.

This command will read the inputs every 5 minutes, and readings are stopped by entering a H (Halt) command.

Alternatively the data can be scaled using a Polynomial, and assigned an appropriate engineering unit (See above, and Section III ñ Scaling Data, Polynomials, Spans and Functions).

Single Ended Measurement Referenced to an External Common

Whenever high level voltages are connected to the dataTaker for measurement as single ended inputs, the positive signal of the high level voltage must be externally attenuated by a resistor network.

High level voltages are connected to the analog input channels as single ended inputs referenced to an external common as follows

 

 

Figure 43 ñConnecting Attenuated High Level Voltages as Single Ended Inputs
Referenced to an External Common

 

Note :  All of the voltage attenuator networks must have the same attenuation factor.

The attenuated single ended voltage is measured between the +ve, ñve or T terminal of the analog input channel and the SE REF terminal. The dataTaker correctly measures the polarity of the input voltage.

Externally attenuated high level voltages connected as single ended inputs referenced to an external common are sampled and the data is returned when a Schedule containing the channel is executed.

The attenuation factor for the voltage attenuator network is specified as a scale factor in the channel options for the input channel, and used to scale the measured voltage.

Using DeTransfer, externally attenuated voltages connected as single ended inputs referenced to SE REF are measured by the command for example

which instructs the dataTaker to measure these inputs on analog input channel 5+ and channel 10ñ.

The voltage measured on analog channel 5+ is attenuated by a 5.5:1 external attenuator network, and so is multiplied by 5.5 before being returned. The voltage measured on analog channel 10ñ is attenuated by a 12.5:1 external attenuator network, and so is multiplied by 12.5 before being returned.

The V indicates that the signal applied to these channels is to be measured as a voltage. The data is returned in units of mV.

The X channel option indicates that the voltage is to measured with respect to an external reference connected to the SE REF input.

Using DeLogger, externally attenuated high level voltages connected as single ended inputs referenced to SE REF can be measured by the same Program Builder program as illustrated above

The single ended connections are selected from the Voltage Wiring Configurations dialog which opens when you have selected the analog input channel, and the attenuation factor is specified via the Attenuation button.

The internal 1 MOhm input termination resistors are not selected during single ended measurement of voltages.

The dataTaker will read the inputs every 15 minutes, and readings are stopped by entering a H (Halt) command.

Alternatively the data can be scaled using a Polynomial, and assigned an appropriate engineering unit (See above, and Section III ñ Scaling Data, Polynomials, Spans and Functions).

Calibrating the External Attenuation Network 

It is not essential to accurately know the resistances of the resistors used to build an external voltage attenuation network.

The attenuation factor for the resistor network can be determined by accurately measuring the input and output voltages using a good quality multimeter.

The voltage attenuation factor of the resistor network can then be calculated by

Voltage Attenuation Factor = V_in / V_out

This approach also has the advantage of taking account of the resistor tolerances, and hence producing more accurate data.

This approach also reduces the need for high precision resistors, allowing readily available resistors to be used. However the resistors used should have a low temperature coefficient.

Measurement Ranges and Accuracy for Attenuated Voltages

High level voltages of virtually any magnitude can be measured using external voltage attenuator networks to attenuate the voltage signal. The maximum input voltage range for high level voltage inputs is

± (attenuation factor x 3.25) Volts

The measurement accuracy for attenuated voltage signals is a function of the tolerance of resistors used in the attenuator network. If 1% resistors are used for attenuators, then this will result in a worst case measurement accuracy of ±2% if the two resistors are at the opposite ends of their tolerance ranges.

Greater accuracy can be achieved by calibrating the external attenuator network, as described above. This approach also reduces the need for high precision resistors, allowing readily available resistors to be used. However the resistors used should have a low temperature coefficient.

Direct Measurement of High Level Voltages

High level voltages of up to ±100 Volts can be measured directly by the dataTaker 505, dataTaker 605, dataTaker 515 and dataTaker 615.

These loggers all have the relay multiplexer which tolerates higher level input voltages, and have an internal attenuator network to attenuate the input voltage to the voltage measurement range of the loggers.

The internal voltage attenuator network is as a four wire attenuator, on each of the +ve, ñve, T and SE REF input lines. The attenuator is located between the relay multiplexer and the analog to digital converter. Therefore the same attenuator is available to all analog input channels.

The internal voltage attenuator network has an attenuation factor of 214.6:1. The internal attenuator resistors are precisely matched during manufacture, to ensure high common mode rejection.

The internal attenuator can be selected and deselected by the two channel options A (Attenuation) and NA (No Attenuation).

Voltage measurement ranges for the dataTaker 505, dataTaker 515, dataTaker 605 and dataTaker 615 data loggers fitted with the relay multiplexer and internal attenuators are as follows

 

Input Type	Differential Channels	Single Ended Channels	Range	Resolution	Accuracy at 25 °C
Voltage ranges without internal attenuator input			±25mV	1µV	0.1%
	10	30	±250mV	10µV	0.1%
			±2500mV	100µV	0.02%
Voltage ranges with internal attenuator input			±7V	250µV	0.3%
	10	30	±70V	2.5mV	0.3%
			±100V	25mV	0.22%

 

Directly Connecting High Level Voltages 

High level voltages of up to ±100 Volts can be directly connected to the dataTaker 505, dataTaker 605, dataTaker 515 anddataTaker 615, and to Channel Expansion Modules (CEM-AD) fitted to these loggers as follows

as differential inputs between the +ve and ñve terminals

as single ended inputs between the +ve, ñve or T terminals and Analog Return

as single ended inputs between the +ve, ñve or T terminals and an external common connected to the SE REF terminal

The direct connections are completed in the same manner as for connecting low level voltages. See Figures 36, 37 and 38 for details.

Reading Directly Connected High Level Voltages

High level voltages directly connected to the analog input channels can be specified in schedule lists in either of two ways in the general formats

nHV
nV(A)

where

n           is the channel number
HV        is the high voltage input type specifier
A          is the channel option to select the internal attenuators

The internal attenuators are automatically selected by the HV input type, and must be selected using the A channel option if the V input type is used.

Using DeTransfer, high level voltages directly connected to the analog input channels are measured by the command for example

which instructs the dataTaker to measure the analog input channels as follows

channel 1 is measured as differential high level voltage

channel 6 is measured as a differential low level voltage with the internal attenuators selected (effectively the same as a HV measurement)

channel 10 is measured as a single ended high voltage between the +ve terminal and Analog Return

Using DeLogger, the high level voltages directly connected to the analog input channels is selected by the radio button  on the Voltage Wiring Configuration dialog

 

 

Other analog input types, such as Current, Current Loop, Frequency and Analog State can select the internal attenuators with channel option A, read inputs with high voltages or high common mode voltages.

The NA channel option will deselect the attenuators for the high voltage (HV) and current loop (L) input types which select the internal attenuators by default.

Over Voltage Protection 

The dataTaker 505, dataTaker 605, dataTaker 515 and dataTaker 615 do not include built in energy absorbing high voltage or lightning protection.

However the analog input channels and the SE REF input are capable of withstanding input voltages as follows

1500 Volt for 10µS

500 Volt for 50mS

100Volt indefinitely.

The Analog Return input can withstand only 5% of these voltages.

The above withstanding voltages apply only to unselected channels. While a channel is being read (a process which typically takes 30mS), these withstanding voltages are reduced to 100 Volt.

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

Where lightning is frequent, we strongly recommend that external energy absorbing lightning protection be wired to each sensor line.

The dataTaker 50, dataTaker 500 and dataTaker 600 can only withstand voltages of 10-15 Volts continuously without damage, and will be damaged by continuous voltages of greater than 20 Volts. However this damage is restricted to failure of the solid state CMOS multiplexer devices, which can easily be replaced.

Error Messages

Voltages at the output of the external attenuator networks (dataTaker 50,500,600) or internal attenuator networks (dataTaker 505, 515, 605, 615) which fall outside the range of dataTaker produce an over-range reading of ñ99999.9 Volt or +99999.9 Volt respectively.

The dataTaker also reports the out of range error condition with the error message ‘E11ñinput(s) out of rangeí if the Messages Switch /M is enabled.

For differential inputs, an over-range condition also results if the difference of the voltages at the +ve and ñve analog input terminals falls outside the above range.