This is a remote location so I would like to use a PC so I can access the plant remotely and be able to make online setpoint or even program modifications. I would like to control refrigerated rooms and engineroom. Could a PC do this better than a PLC? What kind of hardware/software are most standard?

Also there advantages to using thermistors over RTD'd of thermocouples? I believe thermistors have much better resolution and are less expensive.

Thanks
James Baily

 

Addressing only the issue of thermocouples vs thermistors, you are right that thermistors have a larger response. They also don't require special wire as thermocouples do. But they are also more non-linear, unless you buy them together with custom signal conditioning. About the only really big advantange for thermocouples is that they will survive much higher temperature extremes than will thermistors.

Robert Scott
Real-Time Specialties
Embedded Systems Consulting

 

A PC would probably do this more inexpensively for a one off. And with sane software choices, it could do it quite reliably. All the devices mentioned have essentially infinite resolution, The thermistor has the highest sensitivity and thus would require the least exotic circuitry. A fairly pedestrian (cheap) DAQ board would provide high channel count and very good accuracy. But when you add secure remote access into the picture, the PC becomes a no brainer. For a permanent install, I would choose an SBC with DOC and integrated comms and ADC. And in either case I would have a backup thermostat system if the cost of a failure is high.

Regards

cww

 

Measure or log up to 4 thermistors temperature via E-USB directly on your PC and save. Simply connect your electrodes (thermistors) to the corresponding inputs and the USB cable, run the free software and get reading.

See more information on the following links:

Appl. #30:
++++++++++

http://www.eidusa.com/Interface_Boards_Application_30.htm

Kit: 4 thermistors via usb
++++++++++++++++++++++++++

http://www.eidusa.com/Electronics_Kits_EUSB_To_4_THR.htm

Free software (log to file and more):
++++++++++++++++++++++++++++++++++++++

http://www.eidusa.com/Electronics_Kits_EUSB_Software.htm

Good luck,

Ron