Speedy
Mechanical
- Jun 5, 2001
- 229
Folks,
I have a problem with interference on thermocouples.
It goes like this;
We are using K-type thermocouples to measure temp in a block of aluminium. There are a number of single phase cartridge resistance heaters (230v AC with heaters on different phases of 3), a number of solenoid operated water valves (24V DC) and water-cooling channels in the near vicinity of the thermocouple. To make matters worse there are high tension electric mains running directly over the factory roof.
The thermocouple are duplex, one side goes to a CAL temperature controller and the other to a PLC card. The screened extension cables are maybe 2~3metres with both round pin and flat pin connectors along the extension cables. All cables and connectors are K-type.
There are a number of identical machines side by side and on the same metal frame, but there is only the interference with the 1 machine. We replaced all the components with ‘good’ parts from the other machines but the error is still there.
I did a search on this site and found the following helpful thread.
Thread248-91067
Thread239-75319
Thread698-75509
Thread340-75326
Thread240-75320
When we move the round pin plug and socket around the vicinity of the thermocouple the error comes and goes depending on location. I twisted the exposed (unscreened) 1” of cable at the connector and this did correct the Controller reading side but the PLC still reads 60C under the actual temp.
I would appreciate any comments on this as we (including the people that built the machine) have already spent a few days on this.
Q’s as follows;
I gather from the above threads that I should ground all the screening on the cables. It this is the case why don’t the connectors facilitate the connection of the screens?
If there is a problem with electromagnetic fields, why doesn’t it cause problems on the other machines nearby?
If it is the overhead high tension cables, could it be possible to get nodes or localised areas of high field activity?
Speedy
I have a problem with interference on thermocouples.
It goes like this;
We are using K-type thermocouples to measure temp in a block of aluminium. There are a number of single phase cartridge resistance heaters (230v AC with heaters on different phases of 3), a number of solenoid operated water valves (24V DC) and water-cooling channels in the near vicinity of the thermocouple. To make matters worse there are high tension electric mains running directly over the factory roof.
The thermocouple are duplex, one side goes to a CAL temperature controller and the other to a PLC card. The screened extension cables are maybe 2~3metres with both round pin and flat pin connectors along the extension cables. All cables and connectors are K-type.
There are a number of identical machines side by side and on the same metal frame, but there is only the interference with the 1 machine. We replaced all the components with ‘good’ parts from the other machines but the error is still there.
I did a search on this site and found the following helpful thread.
Thread248-91067
Thread239-75319
Thread698-75509
Thread340-75326
Thread240-75320
When we move the round pin plug and socket around the vicinity of the thermocouple the error comes and goes depending on location. I twisted the exposed (unscreened) 1” of cable at the connector and this did correct the Controller reading side but the PLC still reads 60C under the actual temp.
I would appreciate any comments on this as we (including the people that built the machine) have already spent a few days on this.
Q’s as follows;
I gather from the above threads that I should ground all the screening on the cables. It this is the case why don’t the connectors facilitate the connection of the screens?
If there is a problem with electromagnetic fields, why doesn’t it cause problems on the other machines nearby?
If it is the overhead high tension cables, could it be possible to get nodes or localised areas of high field activity?
Speedy