Temp Sensors
Temp Sensors
(OP)
So, what does one use for a clean solution to monitoring air temperature for use in a PLC application?
This is an air conditioning, (that's heating and cooling), system for a local ambient.
This is a 24VDC setup.
This is an air conditioning, (that's heating and cooling), system for a local ambient.
This is a 24VDC setup.
Keith Cress
kcress - http://www.flaminsystems.com





RE: Temp Sensors
Temperature range is easily 0 to 45 centigrades. But can be extended to at least -20 to 75 C. No amplifiers needed. A best-selling application is pool water temperature control with 10 kohm@25C thermistors and a suitable series resistor (22 or 33 kohms) fed from 24 V and taken directy to the AI of a Siemens LOGO! or other low-end PLC.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Temp Sensors
An alternative is a single-chip solution:
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Digital serial output, AND calibrated already. A bit pricier than just a thermistor, but much closer to a PnP solution.
TTFN

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RE: Temp Sensors
I will look further.
IR; Yeah, I could go that way but I really wanted a PnP solution that would have the wire and an assembled protected sensor. This is for very low quantity stats that get ordered intermittently. Having to build sensors every time would be a PITA.
I will be using a brick PLC that has 2 analog inputs.
I'm considering using the other analog input to read an insolation sensor so I can add in comfort offsets.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Temp Sensors
most plc manufacturers have direct interfaces for this sensor.
RE: Temp Sensors
Keith Cress
kcress - http://www.flaminsystems.com
RE: Temp Sensors
These are Siemens products but most companies in the HVAC world will have something similar.
RE: Temp Sensors
I've never seen a simple enough 4 stage temp controller on the market.
I'm looking at just using an LM34. It will take in the 24Vdc and give back 10mV/degree F. I don't think there's anything else out there with that much noise margin. And it's fully linearized too!
Keith Cress
kcress - http://www.flaminsystems.com
RE: Temp Sensors
How about this?
http://
24VDC, different TC's available, 4-20mA or 1-5VDC output, in the temp range you described.
Mike L.
RE: Temp Sensors
That would work perfectly in some of these. However most of these locations are in plenums with 20MPH wind and they state "not for use in fast moving air". Not sure why that would matter but..
Keith Cress
kcress - http://www.flaminsystems.com
RE: Temp Sensors
RE: Temp Sensors
Thanks.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Temp Sensors
RE: Temp Sensors
A normal NTC, that is put in still air shows, say, 10 kohms resistance at 25 centigrades room temperature. If air (still 25 centigrades) is blown across it with a fan, it still shows 10 kohms.
There is a big difference if the sensor is self-heated. Then the air velocity influences thermal coupling and the resulting resistance will change with air velocity.
Make a test! It is easily done - just hook an NTC thermistor in front of a stopped fan to an ohmmeter and note the resistance. Then start the fan and notice that there is no change in resistance.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.