Siemens Analog Input problem

cjd1965

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Hi I was sent to site to look at a fault

The PLC had a 6ES7 331-7Kf02-2AB0 fitted. All the internal square blocks on the card were set to 'C' and the hardware set to 4DMU

The HMI display for the input was showing #######

I removed the cable and used my simulator to read 3.99mA on the field wiring. I injected 4-20mA (source mode) and the HMI display worked fine. I reconnected the cables, ####### displayed.

I connected a pair from a different analog input (approx 6mA, worked fine.

I hooked up meter in series with the plc input, monitored the PIW (PIW moved to DBW xx) and found that with the wire disconnected it showed -32767 and with the 4mA connected it was showing over range of 32767

Any ideas, i have never seen this behaviour before
 
the analogue card is working perfectly - you have proved that.
the 3.99Ma is too low - can you put a meter in series with the actual sensor?
the display on the HMI is either over or under the minimum or maximum setting range (3.99ma??) check if there is a converter somewhere in teh system (PUK) or signal conditioner -
this is possibly where the problem is.
 
Hi
Thanks for the replies

iant the mA is correct at 3.99 (4) because there is no flow (it is a flow meter input)

kalle
The system was working fine last week and the wiring is to the electrical drawings. The -mA is connected directly between the flow meter and the PLC with 1 terminal in the panel. The +mA goes to a perrerl & ****s isolator and onto the PLC.

I have tried bridging the isloator and also tried an isolator that works on a different analog.

--

If I inject from the incoming panel terminals it works fine. With everything reinstated I have 3.99mA on the PLC input and 32767.

I have tried a different analog input wiring into this channel and it works

I have this problem on 2 seperate inputs

Cheers
 
I understand that 3.99 is only just below 4Ma but it is out of range. the 32767 value is an integer value when the card is seeing the incorect values.
You said when you inserted the values with a process meter it worked quite well.
this shows issues with the field wiring.
If you are using a signal converter, it may need calabrating.
the pepperar and Fuchs isolator has some internal adjustments for gain and zero - check these.
 
cjd1965 said:
Hi
Thanks for the replies

iant the mA is correct at 3.99 (4) because there is no flow (it is a flow meter input)

kalle
The system was working fine last week and the wiring is to the electrical drawings. The -mA is connected directly between the flow meter and the PLC with 1 terminal in the panel. The +mA goes to a perrerl & ****s isolator and onto the PLC.

I have tried bridging the isloator and also tried an isolator that works on a different analog.

--

If I inject from the incoming panel terminals it works fine. With everything reinstated I have 3.99mA on the PLC input and 32767.

I have tried a different analog input wiring into this channel and it works

I have this problem on 2 seperate inputs

Cheers
Click to expand...


After what you are telling here, the failure must be in the reference voltage. What voltage do you read between the minus leader(s) and the M-ANA? And to M (0V from PS)? Both should be 0.

You can also disconnect one leader and measure the loop driving voltage. Normally it is 15-24 VDC.

If it's a ghost in there, then you'd better call a shaman.
icon10.gif


Kalle
 
Hi
Firstly, I agree it is a field wiring issue. It is the same if i swap the perrerl and fuchs unit for one from a working channel

I have mA on the card , from the field device. 3.99mA is acceptable. The 32767 is an OVER RANGE issue which I was hoping would lopit to somthing

I think i am going to have to do all continuity checks and earthing checks etc

Cheers
 
Hi Kalle
I think it id a language thing

You mean the analog card 0V and the field device 0V should be the same potential? I agree this should be the case


Cheers
 
Just thinking sideways
is this a new HW setup
if so you may need an additional power module
 
iant, it is at least 5 years old, been in production etc.

Basically a guy there changed a device (different analog input) with power off. When the powered on, that device plus this flow meter both showing 32767 in plc ###### on hmi

I checked all wiring against the schematics and proved the plc card is ok.

Im going to do -ve continuity /potential checks and earth continuity checks tomorrow on site
 
confirm your hardware setup - it sounds like -5 to +5v instead of Ma.
still guessing
 
I already confired I have mA on both problem inputs, and both problem inputs work on with my current simulator


My question really was why i see 32768 over range when i have 4mA on the input.

Cheers
 
Picture is worth a thousand words at this point, me thinks. Can you do a rough sketch of the PLC input, which connections you're using, and the Pepperl & Fuchs isolator? Which isolator is it, a galvanic powered one?
 
Problem Solved - still weird though

Hi All
Returned from site with equipment all running ....yay

I found that the 0V of the 12V DC power supply for the device feeding Analog 4 was not connected to the 0V of the Analog Input Card (the 0V of the 24V supply).

Once i added a new cable, linking the 0V together, it all jumped into life.

The weird thing is that the other input is a 24V device, input 7 so i am at a loss as to why this was affected, and why it worked for 6 years without the link. I am assuming that the earth and 0V of the PSU were linked internally on the original PSU and not on the new one (same type)

Alls well that ends well and thanks for your interest/input
 

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