IO-ATC8 - thermocouple J

[Thiago Röper]

Hello,

Sorry for my english because I'm Brazilian.

I have  IO-ATC8, thermocouples J and a big problems,

 

In measuring up to 50ºC + - is correct, starting this time the value IN PLC increase to 120 + -. More on the measurement sensor is round 70ºC.

[Thiago Röper]

And my temp is 18,5ºC and MI 15 = 185, it is correctly?

[Joe Tauser]

You are correct on the decimal point.  18.5 is returned as 185.  If you don't want the decimal you have to divide by 10 to get rid of it.

If I understand correctly, the value in the PLC is larger than the actual temperature at the probe.  I have had problems with electrical noise getting into thermocouple inputs and causing an offset.  The IO-ATC8 is not electrically isolated.  Are your thermocouple probes grounded or ungrounded?

 

Joe T.

[Thiago Röper]

My thermocouple is simple,

[Joe Tauser]

Use a multimeter to check continuity between the probe tip and either of thermocouple wires.  If you get continuity, it's a grounded probe.  This is how thermocouples are normally made, where the junction is actually part of the tip.  It's perfectly fine until you start getting the problem you are experiencing.

You can buy un-grounded thermocouples, but you have to specify that when you order them.

Your problem is not going to be easy to solve.  I'd start by pulling all the thermocouples out of the machine and raising the temperature of one with an isolated heat source, like a clothing iron.  You'll obviously need a second device to measure the temperature of the heat souce while you try this.  If you find they are accurate when they are out of the machine, then you have an electrical noise problem and the un-grounded units should solve it.

Other suggestions from the forum are certainly welcome.  We are going into hack land here.

Joe T.

[antoinezerafa]

On ‎14‎/‎10‎/‎2016 at 1:44 AM, Joe Tauser said:

Use a multimeter to check continuity between the probe tip and either of thermocouple wires.  If you get continuity, it's a grounded probe.  This is how thermocouples are normally made, where the junction is actually part of the tip.  It's perfectly fine until you start getting the problem you are experiencing.

You can buy un-grounded thermocouples, but you have to specify that when you order them.

Your problem is not going to be easy to solve.  I'd start by pulling all the thermocouples out of the machine and raising the temperature of one with an isolated heat source, like a clothing iron.  You'll obviously need a second device to measure the temperature of the heat souce while you try this.  If you find they are accurate when they are out of the machine, then you have an electrical noise problem and the un-grounded units should solve it.

Other suggestions from the forum are certainly welcome.  We are going into hack land here.

Joe T.

Hi Joe

I have a similar problem. Can I connect a thermocouple directly with v700 or I need to add a module

[Joe Tauser]

You can if you add a V200-18-E3XB to the back of it.  The V700 does not come with an I/O module.  The Samba series SM70-J-TA22 supports thermocouple inputs, but you can't expand it any farther than what it comes with.

The amount of I/O you need for your application should help you decide which route to go.

Joe T.