Siemens analog input 4...20mA

mariobo11

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Hello guys,

I need your help again. Haven't did anything with PLC for a long time, but now I have some little confusion.

Equipement: Siemens 6ES7144-4GF00-0AB0 and pressure transducer is connected to give 4...20mA, 0-300psi.

Pressure transducer is changed with brand new one. I didn't check wiring, but...

Channel 1 is used to read 4...20mA. Raw counts on HMI screen is showing all the time 32767, doesn't matter if pressure is being changed. Is it possible that PLC is showing max raw count if + and - terminals are being swapped???:unsure: Doesn't look like to me, but better to ask professionals.

🍻
 
Well, you say you haven't checked the wiring but you need to.
The specs indicate 12 - 40 VDC with reverse polarity protection, so I wouldn't think (+) and (-) being swapped as an issue but you never know.
The Power supply (+) to the (+) terminal on the transmitter.
The (-) terminal of the transmitter to the analog input module
 
danatomega said:
Well, you say you haven't checked the wiring but you need to.
The specs indicate 12 - 40 VDC with reverse polarity protection, so I wouldn't think (+) and (-) being swapped as an issue but you never know.
The Power supply (+) to the (+) terminal on the transmitter.
The (-) terminal of the transmitter to the analog input module
Click to expand...

Thanks for help, but what could be the reason for reading of 32767?
 
Set your meter on the milliamp scale and put it between the (-) terminal on the transmitter and you analog input card and see what the actual 4-20 mA signal is.
If the signal is connected to the analog input card incorrectly, that could be causing the issue.
 
Sounds like your instrument is wired incorrectly and is therefore applying a high voltage to your analog input. Hopefully this has not yet damaged the input circuitry.
 
Is your instrument configured as 2 wire or 4 wire? You may have voltage from the instrument bucking the voltage from the module. Disconnect the instrument and read if there is voltage from the instrument and from the module. You should only have one or the other. NOT BOTH.
 
No I haven't as I still didn't get any chance for it. Crew is unwilling to stop operation and I'll get my chance probably tomorrow and I want to prepare myself, because they will give me only half an hour. Luckily they have mechanical gauge so they are sure the pressure is good, but on the HMI is not working well. Raw count value is continuously 32767.
 
We don't have info on the barrier module, and that's where the signal is coming from.
I checked the datasheet for the Siemens Analog module, but it didn't give an input impedance. I expect 250 Ohms, but I've seen 500 Ohms with some.
250 Ohm will read 1-5 Volts at input, 2-10 Volts for 500 Ohm.
When troubleshooting, put a meter on terminals 7 & 8. You should have 5 Volts now.
If you have 10 Volts, double the voltages below:
0 PSI = 1 Volt.
75 PSI = 2 Volts.
150 PSI = 3 Volts.
225 PSI = 4 Volts.
 

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