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Current loop connection

The DIVIZE A2007 4-20 mA signal simulators are designed for 2 wire 4-20 mA current loop circuits. When used with an external power supply the A2007 4-20mA simulator can also be used in 4 wire 4-20mA circuits.

2-wire 4-20mA current loop

2 wire 4-20mA loops are mainly used for connecting sensors and actuators over long distances in process control systems, in a 2 wire configuration the power source for the sensor is delivered by the loop, therefore, an extra power supply is not necessary. The DIVIZE A2007 current loop test units can be used in 2-wire 4-20 mA analog current circuits.

In this situation the DIVIZE A2007 current source is passive and the device which receives the current signal is active, the current receiver is the power source for the 4-20 mA wire loop. Check our page about the 4-20 mA potentiometer to see how the A2007 passive current sources work.

connection diagram with 4-20 mA signal simulator for 2-wire usage

4-wire 4-20mA current loop

When used with an external power supply, the DIVIZE A2007 current simulator will act as a current source. In this way the A2007 4-20 mA current source can be used for testing passive equipment such as I/P converters, valve positioners and loop powered displays. For testing 4-wire (passive) PLC and DCS inputs an external voltage source is also required. As shown in the connection diagram below.

connection diagram showing how to connect a current loop tester for 4-wire 4-20 mA systems

In this situation the power for the loop is delivered by the external power supply, thus creating a 4-20 mA signal generator the A2007 simulator controls the current in the loop, the current is received by the connected device.

Special attention is needed for the power supply. Because the current in a 4-20 mA circuit varies, the voltage drop varies with the current. The voltage supplied by the power supply need to be sufficient to compensate the summary voltage drop on all components in the current loop circuit. The voltage drop on resistance components is calculated using ohm's law. The voltage drop on active analog inputs is constant and can be as low as 1 volt.

A2007 4-20 mA simulator connection examples

Below are example connection diagrams for commonly used PLC and DCS systems, also connection examples for valve positioners and I/P converters are provided. The connection of the parts of the loop is only 1 part of a successful 4-20 mA loop, we have gathered more steps for configuring 4-20 mA loops.


A2007 connection to Siemens SM331 module 2-wire.

Hook-up diagram for A2007 4-20 mA simulator and Siemens SM331 analog PLC input card in 2-wire 4-20 mA setup

Siemens PLC systems are commonly used in large process control systems. The SM331 module is designed to convert process variables transported over long distance by means of a 4-20 mA signal to process variables. The Siemens SM331 module is configurable for both 2-wire and 4-wire 4 20 mA usage by means of a plug at the side of the module. The diagram shows how to connect the A2007 4-20 mA simulator when the module is configured for 2-wire 4-20 mA (2DMU) The plug is set to position D. In this configuration the module provides power to the A2007 loop simulator.


A2007 connection to Siemens SM331 module 4-wire.

Hook-up diagram how to use A2007 as 4-20 mA signal generator and Siemens SM331 analog PLC input in 4-wire 4-20 mA setup

When the Siemens SM331 analog input is module is configured for 4-wire 4 20mA usage it does not provide power for the A2007 4-20 mA simulator. The diagram shows how the A2007 units are connected to the SM331 module when the module is configured for 4-wire 4-20 mA (4DMU) The configuration plug is set to position C.

On the Siemens website more information about the SM331 analog input module is available.


A2007 connection to Siemens Logo! AM2 analog input module.

Siemens Logo! AM2 Analog input 2 wire current connection

The A2007 signal simulator shall be connected to the AI1 terminal for Analog input 1 or AI2 terminal for Analog input 2. Both the A2007 and the AM2 Analog input module are passive and therefore require a power source in the loop. This means an additional power supply need to be connected. In the example the power supply for the AM2 module is used as power source for the loop. Therefore the + connection of the A2007 current signal simulator is connected to the 24VDC + terminal (L+) The - terminal is connected to the AM2 module AI1 terminal. The M1 terminal is connected to the M terminal (24VDC return) Current flows from the 24VDC supply through the A2007 simulator, through the Siemens Logo AM2 module back to the 24VDC supply. The A2007 current loop tester is used as 4-20 mA signal generator in this configuration. The signal is measured by the AM2 module en converted in a digital value which is evaluated in the PLC program. More information about the AM2 analog input module can be found on the Siemens website.


A2007 connection to Allan-Bradley 1771-IFE module.

connection diagram for Allan Bradley 1771 analog PLC input module to A2007 signal simulator 2 wire connection

In the schematic diagram above the connection of the A2007 4-20 mA simulator to the Allan Bradley 1771-IFE analog input module is shown. The A2007 4-20 mA simulator is used to set the current in the loop. The Allan Bradley 1771 analog input module convert the current to a digital value which is used in the PLC program and displayed on HMI systems as process value. In this way the A2007 signal simulator can be used to test and validate the PLC program. The Allan Bradley 1771-IFE module does not supply power to the loop. Since the A2007 is a passive device and also does not supply power to the loop an external 24VDC voltage source is necessary. For more information see the manual on the Allan Bradley 1771-IFE analog input module


A2007 connection to Allan-Bradley Micro800 PLC.

Allan Bradley Micro800 2085-IF4 PLC input module connection to 4-20 mA simulator 2 wire connection

The Micro800 PLC comes with passive current inputs. Therefore an external power source is necessary to power the A2007 4-20 mA simulator, the schematic diagram above shows the connection of the A2007 current loop simulator to the Allan Bradley Micro 800 PLC with 2085-IF4 or 2085-IF8 analog input module. The A2007 current loop simulator is used to set the current in the loop, the measured current can be evaluated in the PLC program. The 4-20 mA signal can represent a physical measuring value. See the page about the 4-20mA calculator for more information.


A2007 connection to Beckhoff EL3024/EL3124 analog input module.

Beckhoff EL3024  analog input module connection to 4-20 mA simulator 2 wire connection.

The Beckhoff EL3024/EL3124 is suitable for direct connection of 2-wire 4-20 mA transmitters. Power is supplied from the bus connector on the back-plane. This means the Divize A2007 4...20 mA simulator can connect straight to the terminals on the Beckhoff EL3024/EL3124 module. The EL3024 4...20 mA analog input is using a 12 bit A/D converter so the signal from the current transmitter is transferred to a 12 bit signal in the PLC/IPC. The Beckhoff EL3124 is using a 16 bit A/D (Analog to Digital) converter. This means the EL3124 is more accurate then the EL3024 4...20 mA analog input module.

More information about the EL3024 and EL3124 4...20 mA analog input module is available on the Beckhoff website.


A2007 connection example to Haiwell S04AI/S08AI PLC analog input module.

Haiwell S0AI4 and S0AI8 Analog input connection to 4-20 mA simulator.

The Haiwell S04AI and S08AI are 4/8 input general purpose analog input modules. The modules do not supply power to the circuit so a separate power supply is necessary to provide the loop power. The above diagram shows the connection example. The power supply is used to supply the loop, the current is set with the Divize A2007 4-20 mA simulator. The current is connected to the AIOI terminal on the Haiwell analog input module. Inside the analog input module a 250 ohm resistor is used to convert the 4-20 mA signal to a 1-5V signal. The jumper connection between AIOI and AIOV connection is necessary. This 1-5V signal is converted to a digital number representing the current in the loop.

More information about the S04AI and S08AI general purpose analog input module is available on the Haiwell PLC website.


A2007 connection to Process control system DeltaV AI 16-channel 4-20mA HART card.

Delta-V AI16 HART 2 wire connection diagram

A2007 current loop simulators can be used to test the Delta-V AI 16-channel HART card. This card is provided with a power supply for the connected field transmitters so the A2007 current loop simulator can be connected direct. (The HART functionality is not provided in the A2007 simulator) Only the analog 4-20 mA signal can be simulated with the A2007 simulator.


A2007 connection to Siemens Sipart PS2.

Siemens Sipart PS2 positioner connection diagram

The schematic diagram above shows the connection of the Siemens Sipart PS2 electropneumatic valve controller to the A2007 current loop simulator. The PS2 electropneumatic valve positioner is used to control pneumatic valves based on the 4-20 mA signal. In order to test the positioner the 4-20 mA signal need to be simulated with the A2007 current loop simulator. Since both the valve positioner and the A2007 current loop simulator are passive devices a 24VDC voltage source is necessary to power the loop. See the Sipart PS2 product page on the Siemens website for more information.


A2007 connection to Emerson/Fisher 846 I/P converter.

Fisher 846 I/P converter connection example

In process control systems the Emerson 846 I/P transducer is used to translate a 4-20mA signal in to a pressure signal. The pressure can be used to drive the pneumatic positioner of a control valve. With the A2007 current loop simulator the functionality of the Emerson 846 I/P converter can be actuated. In the circuit diagram the connections are shown. The Emerson 846 I/P converter is powered from the 4 20 mA current loop, also the A2007 is powered from the 4 20mA current loop. Therefore supply voltage shall be provided by a power source. The current will flow from the power supply to the A2007 simulator. The current is controlled by the A2007 simulator and will flow to the Emerson 846 I/P converter where it is evaluated. Then the current will flow back to the power supply closing the circuit. For more information see the manual for the Emerson/Fisher 846 electro pneumatic transducer.

© Divize b.v. ; August 23, 2012 Last update: September 2, 2020.
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