Thermocouple module causing flashing display

[LoggerHead]

I have several Powers 535 controllers controlling verious Processes using a k type thermocouple as the pv. I am needing to input these temp. signals into a AB 5,03 PLC. My plc is located close to the controllers so I just paralled the TC's over to a 1746-NT8 Thermocouple/mV Analog Input Module. It works great except that now my powers controller occasionally will flash a crazy value on the display. Like say it will be a temp. of 235 degrees C and it will momentairly flash 350 or so. It only does it for a split second and isn't causing any problem other then the bugging the control room operator. It does it maybe every 10 sec. or so. Anyone else see this kind of thing? Any suggestion on how to stop it would very welcomed. Thanks in advance.
Daymond

 

[djs]

It might be the open TC detection on the A-B card. If so don't see anyway to prevent it.

 

[buzzp]

TCs can not be hooked in parallel.

 

[CMfgE1]

If you mean the TC's are physically in parallel, djs is right.
You cant physically put them in parallel and expect a proper temp. Your module has 8 inputs. How many TC's do you have?

What kind of TC are you using?

Also is the PLC programmed properly?



Good luck!!!



Quote: "Its not what you know, its who you know"
Everythings a learning experience-Everything

 

[LoggerHead]

When I say that they are parallel, I mean that we have one TC coming in to the prowers controller and it is daisychained over to the PLC. We have TC's daisy chained at other parts of the plant to several devices with out any trouble. We only use it for a lolo alarm and several degrees of inaccuracy is not a real issue. The module shows a good signal and the value in the plc is not jumping at all and read within 2 degrees of the powers controller that it is daisy chained to. Its just that the powers controller will flash on occasion, not enough to cause the controller to try to react to the temp change, just barely enough that you can see it. It is just annoying the operator.

 

[LoggerHead]

Oh yea, its a k type TC reading a temp of approx. 235 deg. C

 

[buzzp]

Other than a faulty unit, it sounds almost like a loose connection somewhere to me.

 

[djs]

Hello;
Try turning off the open TC detection on the 1746-NT8 card.

 

[GTstartup]

Point of info, T/C's Can be connected in parallel, you will just end up with the paralleled temperature readings averaged.

 

[LoggerHead]

Turned out it was being caused by the Open TC detection scan. I disabled this and it is working fine now. Thanks djs and everyone else who took the time to give it some thought. I have used this forum several times and have yet to be dissappointed.
Daymond

 

[CMfgE1]

Yeah - Damn programming - Wel I was somewhat close-
Nice catch djs.

Glad you solved your problem Logger




Later

Quote: "Its not what you know, its who you know"
Everythings a learning experience-Everything