Sensor & PLC conection 4-20mA

Dear Experts,

I have a project using Wago 857-400 and I have a question. Please help me in this case.

6ES7214-1AG40-0XB0 – PLC S7-1200 CPU 1214C DC/DC/DC

6ES7231-4HF32-0XB0 – Module S7-1200, ANALOG INPUT, SM 1231, 8 AI

Wago 857-400 (support 2 cable)

Conductivity sensor (4 wrire with 4 meter cable support).

Now I want to connect sensor to analog module (far away 20 meter)

Is it ok if I use the Wago 857-400 to link sensor & analog module using 4-20mA ?

How to connect 4 wire sensor to Wago 857-400 (Isolator)?

Thank for your support.

JackMac544

Dear Experts,

I have a project using Wago 857-400 and I have a question. Please help me in this case.

6ES7214-1AG40-0XB0 – PLC S7-1200 CPU 1214C DC/DC/DC

6ES7231-4HF32-0XB0 – Module S7-1200, ANALOG INPUT, SM 1231, 8 AI

Wago 857-400 (support 2 cable)

Conductivity sensor (4 wrire with 4 meter cable support).

Now I want to connect sensor to analog module (far away 20 meter)

Is it ok if I use the Wago 857-400 to link sensor & analog module using 4-20mA ?

How to connect 4 wire sensor to Wago 857-400 (Isolator)?

Thank for your support.

 

 Hey JackMac544!!!

unknown user

Is it ok if I use the Wago 857-400 to link sensor & analog module using 4-20mA ?

 Yes it is!!!

Two options, but let me explain you usual meanings/configuration of 2 wire AI card and 4 wire AI card.

When you got 2 wire AI card/module.

1. First wire(maybe it is better to say one wire, it can be either wire out of two of them) is always +24VDC source (with this you supply sensor). That is Us+ in your case.

2. Second wire is Signal +, which means signal + from sensor needs to be connected to the second AI slot. That is IN+ in your case

When you got 4 wire AI card/module.

 1.  First wire L+

2. Second wire M-

3. Third wire Signal + (from sensor)

4. Fourth wire Signal - (from sensor)

(with 4 wire sensor L and M are usual marks for power supply)

Solution for your task(2 wire AI card/module.), there are two options.

1.First solution

1.1.First wire:  You can supply sensor directly from your module +24VDC. Just make sure your AI card gots enough power to supply sensor. So connect Wago Us+ to the sensor L+

1.2. Second wire: Connect sensor Signal + terminal to the Wago IN+

1.3. Third wire: Since you want to connect 2 wire AI card with 4 wire sensor you need to connect third wire as well. You need to have common minus from sensor and AI card, so connect Sensor M- to the AI card Signal- (signal minus) and to the WAGO AI GND 3 terminal. GND 1 and GND 3 terminals should be internally interconnected, if that is not the case, connect them as well. 

2. Second solution: You can supply your sensor from outside source, for example from some MCB inside your control cubicle. So lets say you decided to supply sensor from miniature circuit breaker F23.

First wire: Connect F23+ to the sensor L+

Second wire : Connect F23- to the sensor M-

Third wire : Connect Sensor Signal + to the Wago IN+

Fourth wire: Connect F23- with the Wago GND 1 and with Sensor -(minus) terminal.

You use second option once your AI module has got not enough power to supply sensor, and usually 4 wire sensors requires more Amps / Power than 2 wire sensors, so if you choice second option you can not be wrong.

If you got more questions, just shoot!!!

Dear My Friend,

Thank you for your information. It helps me a lot.

{snip}

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For follow up question see: connect to PLC via RS485: I don't have static IP, my solution is use Teamview VPN.