S7-1200 Type K Thermocouple.

Mike_RH

Lifetime Supporting Member
M
Join Date
Sep 2006
Location
Toronto
Posts
896
Hi All,

I have a S7-1214 with the 4 channel TC signal module.
All 4 channels are in use with Type K TC's

The S7-1200 System manual indicates that the temperature should be in the IW for each channel must multiplied by 10. E.G. 20 degrees = 200.

I am getting a value of ~1050 for ~68 degrees F.

Any suggestion's?
 
A length of thermocouple wire with both ends at ambient temperature has no temperature gradient and therefore produces no EMF, it's output = 0.0mV.

A length of copper wire connected across the + and (-) terminals is the equivalent circuit, 0.0mV.

Either of the above should produce an ambient temperature value from a thermocouple card, because the terminal voltage, 0.0mV, is added to the cold junction compensation measurement (the temperature of the connection terminals). The terminal temperature is probably close to room temperature.

I'm not a Siemens guy, but this tells me that the cold junction is not configured or implemented properly, maybe because the channel or the card is not configured or setup properly. Doesn't Siemens have some short of doodad on the outside of the card that has to be pushed or pulled to one position or another?
 
Thanks for the response.

All the configuration is done through software.
Which looks good.

The input responds to temperature changes, it's just reporting the wrong value.

I will try shorting an input channel on the module tomorrow and see what we get.

Thanks
 
I'm certain when we figure it out, it will be smack your head and scream "I'm an idiot" moment! But for now it's annoying.

I think at one point today I tried the to read a channel in voltage mode, and got the same result. Which confused me.

I'll check the config again tomorrow.
 
If the thermocouples are grounded and the card is single ended with little or no isolation, then you could be seeing one or more ground loops which manifest themselves as an offset. The offset usually gets worse, the more thermocouples and grounding points that are added.

If you don't know whether the thermocouples are grounded you can check by putting an ohmmeter between either lead and the sheath (when the T/C is disconnected from the AI terminal strip). Ungroundded is an open circuit, grounded is very low resistance.
 
Reverse polarity for T/C's drives the signal in the opposite direction, so any positive temperature appears as a negative and the hotter it gets the more negative the readings go.

His is way upscale from where it should be, so it's not likely reverse polarity.
 
The channels are set to thermocouple, type K.
Click to expand...
So if you had a Type J thermocouple connected, it might read something like 1050. What is the color of the individual wires inside the cable? That will tell you what type of TC it really is. I remember that Type K is yellow and red (at least in the US and Canada). I think Type J is white and red. Any other colors mean that you have the wrong type of TC (or the module is configured for a TC that does not exist).

Thermocouples do go bad, open up, or the wire insulation burns off and shorts to the sheath or to some other ground. A shorted TC can still give you a reading, but a wrong one.
 
Last edited:
It isn't clear to me whether the value is 105.0, 1050 or 10500, because I'm not sure what got/gets multiplied by ten.

If "wire break diagnostics" (what the rest of us call burn-out) is enabled, then a value of 10500 might be a burn-out temperature. Conventional up-scale burn-out drives the indicated to an artificial maximum value to indicate sensor failure or open circuit. I'm not sure if Siemens is conventional or not.
 

Similar Topics

S
Issue with S7-1200 Type K Thermocouple
Dear experts, I am using a Thermocouple K type and connected to a SM 1231 signal board (6ES7 231-5QD32-0XB0) controlled by a S7-1200 PLC. In my...
Replies
4
Views
2,133
rootboy
rootboy
id10t_error
1762 Micro logix 1200 Ver.C Memory Type?
What type of internal memory does the MicroLogix 1200 Ver.C have? In the documentation, there is only an internal non-removable battery for the...
Replies
1
Views
1,583
rupej
R
H
TIA V14 - S7-1200 POINTER Data Type
Hi all, Can anyone tell me if the POINTER data type is available in TIA for S7-1200 and what the format looks like? It's not listed under Data...
Replies
2
Views
4,133
Lare
L
U
Filtering Date out of DTL type in S71200
Hellow, I'm busy with a little program that evaluates per day independent from the date, only the time matters. I do comparing with DTL. I...
Replies
2
Views
1,732
userxyz
U
R
s7 1200 indirect addressing using real data type
Hi, Im new to SCL, but decided to start learning it - if only to be able to do some simple jobs such as indirect addressing. got some simple...
Replies
3
Views
6,902
Rob.Hill
R
Back
Top Bottom