Wrong Select: Modul select 0 -20 mA to Device 4 - 20 mA

Herbrata

Member
Join Date
Mar 2016
Location
Indonesia
Posts
6
Hi I am nubie from jakarta, indonesia,
sorry for my english.

I work with S1200 PLC, and an analog input modul.
I select wrong input scale, a 0 - 20 mA in modul, connect to 4 -20 mA Temperature Transmitter.

Recently my channel modul is broken, the integer output value standstill at 4070 no matter the value of current (but when no signal from transmitter, the output integer is 0).

Can this wrong selective mode of 0 - 20 mA in module cause the broken channel in analog input modul?

Please someone help.
 
Hi I am nubie from jakarta, indonesia,
sorry for my english.

I work with S1200 PLC, and an analog input modul.
I select wrong input scale, a 0 - 20 mA in modul, connect to 4 -20 mA Temperature Transmitter.

Recently my channel modul is broken, the integer output value standstill at 4070 no matter the value of current (but when no signal from transmitter, the output integer is 0).

Can this wrong selective mode of 0 - 20 mA in module cause the broken channel in analog input modul?

Please someone help.


Hi, and welcome to the forum!

Some questions to clarify:

- Has it ever worked OK?
- Is the device 4 or 2 -wire? (2 wire means that it is loop powered from an external source (the PLC card), 4 wire means that the device has its own power source.


The Simatic analog input cards are in my experience quite robust, and I have seen lots of double powered loops where the input channels have survived.

Kalle
 
Hi, and welcome to the forum!

Some questions to clarify:

- Has it ever worked OK?
- Is the device 4 or 2 -wire? (2 wire means that it is loop powered from an external source (the PLC card), 4 wire means that the device has its own power source.


The Simatic analog input cards are in my experience quite robust, and I have seen lots of double powered loops where the input channels have survived.

Kalle
- Has it ever worked OK?
__ Yes, it worked OK before.

- Is the device 4 or 2 -wire?
__ It is 2 wire device.

I think my problem is coming from Ground Loop.
 
It is not clear to me exactly what the symptoms of the problem are.

Apparently you get 4070 counts(?) when the transmitter is connected. 4070 is what percentage of the scale? (I'm not a Siemens guy, I'm an instrument guy).

When you disconnect the transmitter the system shows 0, which one would expect.

Why do you think the problem is with the input channel/module but not the transmitter?

Have you put a milliammeter in series in the circuit to observe the change in loop current?

Have you tested the analog input with a 4-20mA source other than the transmitter? A simulator or a different transmitter?
 
Herbrata selecting a 0-20mA Input Module scale will work fine with a 4-20mA transmitter.
It will Not cause any damage.

Move a good, working transmitter from a different input to this one you want to check.
You should see the same integer value on both inputs.

I doubt the problem is the input card.
 
I can't say for sure with a Siemens PLC, but with some Allen-Bradley analog input cards, the lowest value they will display is 3.2mA. Even if you have nothing connected to it, it will read 3.2mA.

If your analog input card is similar, there could be an open circuit in the wiring and there is actually no current flow at all.

The suggestions above are all good ones, insert a mA meter into the circuit and measure the actual current flow, and try wiring a known good 4-20mA source - whether that be another sensor, or a loop calibrator - directly into the analog input and see what results you get. With that information we can probably help narrow down the problem a little better.
 
It is not clear to me exactly what the symptoms of the problem are.

Apparently you get 4070 counts(?) when the transmitter is connected. 4070 is what percentage of the scale? (I'm not a Siemens guy, I'm an instrument guy).

When you disconnect the transmitter the system shows 0, which one would expect.

Why do you think the problem is with the input channel/module but not the transmitter?

Have you put a milliammeter in series in the circuit to observe the change in loop current?

Have you tested the analog input with a 4-20mA source other than the transmitter? A simulator or a different transmitter?
Before work okay.
4 - 20 mA read = 5500 - 27648 in integer value reading in PLC.
Now the transmitter still send 4 - 20 mA, but the integer reading value stay in about 4000 - 4700.
 

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