Sensing temp without transmitter to PLC input?
Sensing temp without transmitter to PLC input?
(OP)
Anyone know of a temperature probe with mA or V output, that doesn't require an $80 transmitter? The purpose here is to read a temperature 60-150 degF and send it to an analog PLC input.
Must be a way to do this without spending big bucks.
After all, I have a temp sensor in my house with digital readout that costed $10!
Must be a way to do this without spending big bucks.
After all, I have a temp sensor in my house with digital readout that costed $10!
Nic Van Engen
Electrical Technician





RE: Sensing temp without transmitter to PLC input?
Plesae read FAQ240-1032
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RE: Sensing temp without transmitter to PLC input?
RE: Sensing temp without transmitter to PLC input?
accuracy of 2% per 100 degF and precision of 1 degF increments is sufficient.
Repeatability & consistency is more important. The sensor will never be calibrated or tested for accuracy (after intitial testing & production) so it needs to stay within the 2% accuracy as long as the equipment is in service (many many years).
I've found after shopping around for temp sensors that these kind of specs are easy to satisfy, it's input-ing the info to the PLC that is the challenge (as far as cost is concerned).
Nic Van Engen
Electrical Technician
RE: Sensing temp without transmitter to PLC input?
The trouble is that a Pt-100 (thermocouple/RTD ready) analog module isn't any cheaper than a transmitter (as a general rule), and is capable of ONLY temperature inputs. Main advantage at that point would be asthetics & easier setup.
I agree that if I were in need of 2 or more temperature inputs, (or more PLC inputs altogether) that would be a good way to gain some and therefore MUCH more cost effective than a transmitter.
Nic Van Engen
Electrical Technician
RE: Sensing temp without transmitter to PLC input?
http://www.national.com/ds/LM/LM35.pdf
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RE: Sensing temp without transmitter to PLC input?
I have been using them in white-goods like bath-room fans, in industrial equipment lige spot-welders and a few other products that I have designed over the years.
They are non-linear, yes. But linearization to better than +/-2 degrees celsius is possible (it will cost you a simple resistor) over your temperature range. The output voltage can usually be taken to several volts without introducing self-generated heat errors.
This gives you some ideas: ht
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Sensing temp without transmitter to PLC input?
Yes. They are non-linear. But it doesn't cost you more than a simple resistor to have the +/-2 degree celsius you need over that temperature range. It will, in fact, be better than that.
The output voltage can easily be in the "several volts" range without introducing self-heating errors. The output signal can be filtered with an easy capacitor across your PLC input (no resistor needed, the NTC+R is the resistor).
They exist in many shapes. There are even some in teflon and stainless steel housings. And still at a low low cost.
ht
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Sensing temp without transmitter to PLC input?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...