RTDs as heating elements?

[Steve Lieberman]

Someone on my project suggested using an RTD as a heating element;
they claimed one could supply the RTD with a constant current (and
allow unlimited voltage) and that should allow for a somewhat constant
temperature.

Does this make sense? Is it reliable?

Thanks,
Steve

 

[Spehro Pefhany]

Someone on my project suggested using an RTD as a heating element;
they claimed one could supply the RTD with a constant current (and
allow unlimited voltage) and that should allow for a somewhat constant
temperature.

Not really, as the RTD only varies about 0.4%/K around room
temperature, but you could certainly control it so that it runs at a
constant temperature. Or a constant current. But not both.

Does this make sense? Is it reliable?

You could always ask the RTD manufacturer. ;-)

A resistor makes a much cheaper heating element.

Best regards,
Spehro Pefhany

 

[John Larkin]

Not really, as the RTD only varies about 0.4%/K around room
temperature, but you could certainly control it so that it runs at a
constant temperature. Or a constant current. But not both.


You could always ask the RTD manufacturer. ;-)

A resistor makes a much cheaper heating element.

Best regards,
Spehro Pefhany

It is feasible to use the RTD for both functions, heating and sensing,
simultaneously, *if* that makes sense thermally. It pretty much does
only for large-area etched-serpentine type heaters that are glued onto
the gadget to be heated. Minco does this.... I think they have some
appnotes on the technique.

Seems like a cute trick/lot of trouble to me. I agree that heaters and
sensors should generally be different things.

A ceramic PTC element, run at constant voltage, gives fairly good
temperature regulation... reduces delta ambient effects by 10:1 or so
maybe.

Could you drive a PTC from a negative resistance source and improve
temperature regulation?

John

 

[Spehro Pefhany]

Seems like a cute trick/lot of trouble to me. I agree that heaters and
sensors should generally be different things.

Yes they generally should be. I've done it for good reason, kind of
the thermal analog of the typical high-speed photodiode amplifier.

A ceramic PTC element, run at constant voltage, gives fairly good
temperature regulation... reduces delta ambient effects by 10:1 or so
maybe.

Could you drive a PTC from a negative resistance source and improve
temperature regulation?

Sure, but I think that amounts to the same thing as above.

Best regards,
Spehro Pefhany

 

[John Larkin]

Sure, but I think that amounts to the same thing as above.

Oh, yeah. Right. Duh.

John

 

[Tony Williams]

Someone on my project suggested using an RTD as a heating
element; they claimed one could supply the RTD with a constant
current (and allow unlimited voltage) and that should allow for a
somewhat constant temperature.

A simple bridge circuit can be used to force the RTD to a
constant resistance. This automatically forces it to a
a constant temperature.

 

[Rene Tschaggelar]

Someone on my project suggested using an RTD as a heating element;
they claimed one could supply the RTD with a constant current (and
allow unlimited voltage) and that should allow for a somewhat constant
temperature.

As non-native english speaker : what is an RTD ?

Rene

 

[John Larkin]

As non-native english speaker : what is an RTD ?

Rene

Resistor, Temperature Dependent. Most commonly, these are 100 ohm
platinum-wire elements used as very precise temperature sensors, used
commonly in industry and science. Also available in platinum
thin-film, and occasionally with other metals, like copper. Google
"platinum RTD" for more.

John

 

[Spehro Pefhany]

As non-native english speaker : what is an RTD ?

Resistance Temperature Detector. A precision wire-wound or thin-film
metal resistor that has a predictable temperature-resistance
relationship. Often made from platinum, but also nickel, various
base-metal alloys, copper. Not the same thing as a thermistor, the
change per degree is much less, typically around +0.39%/K at room
temperature (roughly PTAT).

Perhaps "Platin Widerstandsthermometer" would be a familiar term for
you?

Best regards,
Spehro Pefhany