PTC & NTC Probes.

[Testech]

Can anyone give advice on the correct way to test PTC & NTC probes please.

[chillin out]

Check the resistance against a table supplied by the manufacturer.

Chillin

[Testech]

Check the resistance against a table supplied by the manufacturer.

Chillin

This question is in the general sense.
I was asked today at an interview how I would go about testing a NTC or a PTC probe.

[Brian_UK]

I was asked today at an interview how I would go about testing a NTC or a PTC probe.

And your answer was ??

[Testech]

Can anyone give advice on the correct way to test PTC & NTC probes please.

We all know that "Thermistors" convert heat energy into measurable electric signals, but how can I truly check if a PTC or NTC probe is actually working ?.

[Testech]

And your answer was ??

As I have never actually changed a PTC or NTC probe, I couldn't offer any advice on actual testing.
I know one measures decreasing heat and one rising heat, but with a table or a spec sheet, how would I actually get a yes or no working reading ?

[Testech]

As I have never actually changed a PTC or NTC probe, I couldn't offer any advice on actual testing.
I know one measures decreasing heat and one rising heat, but with a table or a spec sheet, how would I actually get a yes or no working reading ?

Thats WITHOUT not WITH !

[Brian_UK]

A quick look around the web seems to show that a set voltage will give a set resistance.

Have a read here, maybe it will help...

A glossary slightly modified from that given in a US government publication: MIL-PRF-23648D. Note that the term being described is in bold typeface.

A thermistor is a thermally sensitive resistor that exhibits a change in electrical resistance with a change in its temperature. The resistance is measured by passing a small, measured direct current (dc) through it and measuring the voltage drop produced.

The standard reference temperature is the thermistor body temperature at which nominal zero-power resistance is specified, usually 25°C.

The zero-power resistance is the dc resistance value of a thermistor measured at a specified temperature with a power dissipation by the thermistor low enough that any further decrease in power will result in not more than 0.1 percent (or 1/10 of the specified measurement tolerance, whichever is smaller) change in resistance.

The resistance ratio characteristic identifies the ratio of the zero-power resistance of a thermistor measured at 25°C to that resistance measured at 125°C.

The zero-power temperature coefficient of resistance is the ratio at a specified temperature (T), of the rate of change of zero-power resistance with temperature to the zero-power resistance of the thermistor.

A NTC thermistor is one in which the zero-power resistance decreases with an increase in temperature.

A PTC thermistor is one in which the zero-power resistance increases with an increase in temperature.

The maximum operating temperature is the maximum body temperature at which the thermistor will operate for an extended period of time with acceptable stability of its characteristics. This temperature is the result of internal or external heating, or both, and should not exceed the maximum value specified.
.
The maximum power rating of a thermistor is the maximum power which a thermistor will dissipate for an extended period of time with acceptable stability of its characteristics.

The dissipation constant is the ratio, (in milliwatts per degree C) at a specified ambient temperature, of a change in power dissipation in a thermistor to the resultant body temperature change.

The thermal time constant of a thermistor is the time required for a thermistor to change 63.2 percent of the total difference between its initial and final body temperature when subjected to a step function

The resistance-temperature characteristic of a thermistor is the relationship between the zero-power resistance of a thermistor and its body temperature.

The temperature-wattage characteristic of a thermistor is the relationship at a specified ambient temperature between the thermistor temperature and the applied steady state wattage.

The current-time characteristic of a thermistor is the relationship at a specified ambient temperature between the current through a thermistor and time, upon application or interruption of voltage to it.

The stability of a thermistor is the ability of a thermistor to retain specified characteristics after being subjected to designated environmental or electrical test conditions.

[monkey spanners]

Warm them up and cool them down and see if the resistance changes, as Chillin says you will need a chart to check e.g. 1200 ohms at 20 c 400 ohms at 5 c.
Or put a new one on and see if its reading the correct temperature now. It would be wise to check what offsets have been programed into the control the probe is wired to as it may have been adjusted for whatever reason.

Or do as Brian says.......MUST TYPE QUICKER

Jon

[Brian_UK]

Or do as Brian says.......MUST TYPE QUICKER

Jon

It was supposed to be a web link but I had done a cut'n'paste instead; you don't think that I typed all that myself did you

[Grizzly]

Hi Testech.
Follow the link supplied below.
Download Tech Bulletin No 15.
And on the first page of 21 detailed pages is how to test ntc and ptc probes.
Grizzly
http://www.invensyscontrolseurope.co...lBulletins.htm

[Testech]

Thank's Guys, I sure have a lot of info to work on now !

[Peter_1]

The answer they expected was perhaps simple, when warming up the sensor, the resistance increases for a PTC and decreases for an NTC.

Most modern small controllers like Eliwell, Dixell accept both and you have to program this in the instrument.

Eliwell NTC's have a blue wire and PTC a grey wire.

If you connect a PTC to a controller which was programmed for an NTC you will see +/- 110°C (230°F) for +/-20°C (68°F) ambient.

[chillin out]

We all know that "Thermistors" convert heat energy into measurable electric signals, but how can I truly check if a PTC or NTC probe is actually working ?.

I for one have never measured the electric signals on a ntc/ptc probe.
And I don't think anybody else would carry a meter that could measure it either.

I still think my first answer is the only way to do it, which is also the way we all do it in the field.

Chillin

[chemi-cool]

Very simple.....

PTC is 1k ohm

NTC is 10K ohm

Chemi

[nike123]

Very simple.....

PTC is 1k ohm

NTC is 10K ohm

Chemi

It is not that simple!
http://www.specsensors.com/pdfs/ntc_...ring_notes.pdf

http://www.specsensors.com/pdfs/ptc_...ring_notes.pdf

[philfridge]

I for one have never measured the electric signals on a ntc/ptc probe.
And I don't think anybody else would carry a meter that could measure it either.

I concure , what is all the fuss about why dont you just wire into the controller and if its faulty it will come up E2 or PF1 etc then you change it for a new one either ptc or ntc. Nobody meters them ??

[steve62]

Wow, just change the probe. I dont have the time to mess around on site and would be surprised if you all did. I mean that in the nicest possible way of course!!