TC to RTD

[JaJos]

We are using A Watlow D-8 to control 8 heaters. The D-8 uses 100ohm RTD inputs for control. During final assembly of the the prototype, we discovered 2 of the heater only have TCs.

Does anybody know of a way to convert a TC to RTD signal or if it is even possible?

Thanks in advance
js

 

[VEBill]

Any of these help?

http://www.clrwtr.com/ABB_Analog_Signal_Converters.pdf

I didn't see an RTD output, but I didn't check carefully...

 

[itsmoked]

I don't get it.. Can you not just tell the DC which two are T/Cs and be done with it?? Most of these high end multi-loop PID controllers allow all sorts of different inputs.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

From the D8 spec sheet at:

http://www.watlow.com/literature/specsheets/files/controllers/anad80902.pdf

Analog Inputs
• Thermocouples: User selectable type, direct connection,
linearization, reference junction compensation, reversed
and shorted T/C detection and upscale break protection
with output averaging.
• RTD: 2 or 3 wire, platinum, 100? @ 0°C, DIN curve.
Requires scaling resistors. See special inputs in ordering
information.
• Linear: current and voltage signals from linear transmitter
Input Range and Accuracy
Sensor Range (°C) Range (°F) Accuracy
Type B 66 to 1760°C 150 to 3200°F ±4.0°C
Type E -200 to 787°C -328 to 1448°F ±1.0°C
Type J -212 to 760°C -350 to 1400°F ±1.2°C
Type K -268 to 1371°C -450 to 2500°F ±1.3°C
Type R -18 to 1766°C 0 to 3210°F ±2.8°C
Type S -18 to 1760°C 0 to 3200°F ±2.8°C
Type T -268 to 399°C -450 to 750°F ±1.6°C
RTD -200.0 to 621.1°C -328.0 to 1150.0°F ±0.5°C

I don't have time to dig out the specifics, but there's some means of configuring it to take a thermocouple.

Do you know what type thermocouple you are working with?

Dan

 

[Mike2468]

In the fine print of the part number page: describe any non-thermocouple input channels for "factory installed resistors". (To me, factory installed might mean surface mount components on the PCB. This is more difficult to update than resistors hanging on the input connectors.)

Apparently, the Watlow does not have an universal input circuit. I am sure that they have a reason, but I can't imagine why.

I would recommend installing 2 RTDs in your heaters, and keeping all of the Watlow channels identical. Otherwise, somebody will mix up the channels some day.

 

[danw2]

Good observation, Mike. Input selection is dependant on installed hardware on the board.

Pages 190 to 193 (pdf) of the D8 manual describe the input scaling resistors for field changes. Thermocouples use a "0 ohm resistor".

Page 149 (pdf) shows the configuration selection for TC type.

manual at:

http://www.watlow.com/literature/prodtechinfo/files/controllers/d8_eng_2.pdf

Dan

 

[Mike2468]

Page 190-193 of the manual? A 232 page manual for a loop controller? Wow.

 

[itsmoked]

Those used to be Anafaze controllers before being slurped up by Watlow. I used to make them modify the firmware for the insane things my customers wanted. I never liked the designs but they were often the only game in town. They are pretty complex!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com