Cart

Empty

£0.00

Shopping cart is empty

Login/Register

To prevent automated spam submissions leave this field empty.

+44 (0) 191 387 1923     peak.test@thepeakgroup.com

Map

Map replacement

Location

Peak Test Services Ltd

152a Front Street
Chester-Le-Street
Co. Durham
DH3 3AY
United Kingdom

peak.test@thepeakgroup.com
+44 (0) 191 387 1923
+44 (0) 191 387 1994

Contact Us

News

Peak Test Services can now provide a new
The blocking tester is a special tool to detect b

About Peak Test

Founded in 1986, Peak Test is the UK leader in the distribution of test probes and receptacles, it carries the most comprehensive range of probes, many of which are available ex-stock for next day delivery.

Peak Test are the UK distributor for Virginia Panel Corporation (VPC) Mass Interconnect, Optomistic LED Test and Voltera Prototype PCB Printer.

Peak Test Services is an ISO accredited Company.

The leading UK distributor of Spring Contact Test Probes and Test Accessories

DRA004 - DRA009 General Application Note

Click here to download PDF of this page

Generic 3 Channel Isolation Amplifier

The DRA range are DIN Rail mounting generic 3 channel isolation amplifier that can be configured during manufacture. Standard options are offered with 3 types of inputs, External Current Shunt, Internal Current Shunt and Internal Voltage Divider. It can also be offered as a customised unit with the input scaling and configuration defined by the user.

The Reason for Isolation

The DRA004 isolation amplifier provides a means to measure signals without the signal ground and measurement ground being directly connected. This is desirable in a number of instances in industrial applications:

  • The signal is referenced to a ground at a different potential to the measurement system ground
  • The signal has a large common mode swing relative to the measurement system, for example a current sense resistor in an electrical phase
  • Break ground loops so that leakage currents cannot flow in either direction between the signal and the measurement

Voltage and Current Measurement

The DRA004 isolation amplifier has been designed to measure voltage or current. It has 3 identical channels that can be configured to measure anything from millivolts full scale up to ±1000V full scale. The signal may be voltage from an electrical supply, the phase of a motor, a solenoid drive, or it may be a voltage derived from a sensor such as a current sense resistor.

The block diagram shows 3 identical channels. The key components that confer the property of isolation are the IsoAmps and the IsoDCs. The IsoAmps components are integrated circuit isolation amplifiers with a fixed gain of 8.2 between the differential input and the differential output. The PCB has been designed to allow the maximum isolation voltage between input and output of 1410V.  The IsoDC components are DC to DC power supplies that create an isolated 5V rail for the input stage of the IsoAmp component. The IsoDC parts have an isolation rating of 1500V so the overall rating of the DRA004 is 1410V between the input and the output. The input channels are isolated from each other and the PCB layout ensures that the 1410V isolation is maintained between channels on the input side. On the output side, the channels are referenced to Vref which is internally connected to the supply 0V. The outputs should be connected to a differential input of the data acquisition system.

In the block diagram, the GainAmps are instrumentation amplifiers that set the overall scaling of the DRA004. The supply voltage is ±5V and the output can be scaled within that range; however for the standard variants the output range is ±2V to be compatible with a standard range of National Instruments DAQ sub-systems. Also ±2V can be configured for a 5V ADC on a microcontroller. Nevertheless, the output can be configured for other customised scaling levels within the ±5V limit.  Note that the isolated 5V supplies for IsoAmp components are derived from the +5V input rail.

The BufferAmp components have a gain of 1 and provide the drive for output cables and short circuit tolerance.

Input Network Standard Variants

Fig 2. Input Network Variants

Customisation

The input network can be factory built to suit the user on request. The PCB has the following limitations:

Fig 3. Custom input network.

The network on the input of each channel can be defined to provide an input to the IsoAmp of up to ±200mV. The IsoAmp has a fixed gain of 8.2 and the gain of GainAmp, see Fig 1, can be set by RG on each channel according to gain = (1+(100k/RG)).

The bandwidth is set by an RC network at 80kHz. This can be set to any bandwidth up to 200kHz – see below.

* ±200mV is the maximum measurable input to the isolation amplifier. ±2V is the maximum without damage and ±6V is maximum transient for 2secs.

Offset Trim

There is an offset adjustment potentiometer on each channel that is accessible by lifting the top cover of the DIN Rail case.

Bandwidth and Noise

The standard variants have a simple RC limit to the bandwidth set to 80kHz. The maximum bandwidth is limited by the IsoAmp at 200kHz and by the GainAmp as a function of frequency (500kHz at G=4, 100kHz at G=10, 80kHz at G=20).

Typically the output noise is 2.5mVrms at 0V input and is due mostly to the IsoAmp component.

There is a 100R resistor in the output that can be used to reduce the bandwidth by placing a capacitor across the output terminals or in the measurement equipment. As a customised feature the capacitor can be fitted on the PCB on through-hole pads.

Typical Connections

DRA005, 3 channel external current shunt

The DRA005 module has 3 channels configured as Type A in Fig2 above. The current shunts are labelled RSense and fit in the phase connection. This could be an electrical supply phase or the phase supply of a motor. The DRA005 is scaled to accept ±50mV full scale to produce ±2.0V output. The Murata/Datel 3020 series of shunts are available in 50mV full scale and the correct model should be chosen to match the current to be measured. If say ±200A peak is chosen as the full scale then 1A will be the minimum current that can reasonably be measured. The bandwidth is DC to 80kHz so this arrangement could be used to measure the phase current of high speed motors, variable frequency aircraft supply systems, 50/60Hz electrical systems, DC solar power systems or DC solenoids, for example. 

The 0V supply to the DRA005 and to the DAQ should be referenced to a star point in the measurement rack and can be earthed at the star point.

DRA006, 3 channel internal current shunt

The DRA006 module has 3 channels configured as Type B in Fig2 above. The current sense resistor is internal and is in the phase connection. This could be an electrical supply phase or the phase supply of a motor. The DRA006 is scaled to ±20A full scale to produce ±2.0V output. The bandwidth is DC to 80kHz so this arrangement could be used to measure the phase current of high speed motors, variable frequency aircraft supply systems, 50/60Hz electrical systems, DC solar power systems or DC solenoids, for example.  The 0V supply to the DRA006 and to the DAQ should be referenced to a star point in the measurement rack and can be earthed at the star point.

DRA007, 3 channel voltage

The DRA007 module has 3 channels configured as Type C in Fig2 above. The voltage divider resistors are internal and connect to the phases. This could be an electrical supply phase or the phase supply of a motor. The DRA007 is scaled to ±1000V full scale to produce ±2.0V output. The bandwidth is DC to 80kHz so this arrangement could be used to measure the phase current of high speed motors, variable frequency aircraft supply systems, 50/60Hz electrical systems, or DC solar power systems for example.  The 0V supply to the DRA007 and to the DAQ should be referenced to a star point in the measurement rack and can be earthed at the star point.

DRA008, Single phase voltage and external current shunt

The DRA008 module has 1 channel configured as Type A and 1 as Type C in Fig2 above. The voltage divider resistors are internal and connect to the phase. The current shunt is labelled RSense and fits in the phase connection. The bandwidth is DC to 80kHz so this arrangement could be used to measure the phase current of high speed motors, variable frequency aircraft supply systems, 50/60Hz electrical systems, or DC solar power systems for example.  The 0V supply to the DRA008 and to the DAQ should be referenced to a star point in the measurement rack and can be earthed at the star point.

DRA009, Single phase voltage and internal current shunt

The DRA009 module has 1 channel configured as Type B and 1 as Type C in Fig2 above. The voltage divider resistors are internal and connect to the phase. The current sense resistor is internal and is in the phase connection.  The bandwidth is DC to 80kHz so this arrangement could be used to measure the phase current of high speed motors, variable frequency aircraft supply systems, 50/60Hz electrical systems, or DC solar power systems for example.  The 0V supply to the DRA009 and to the DAQ should be referenced to a star point in the measurement rack and can be earthed at the star point.