Measuring temp. of rotating body inside closed assy.

[daninacan]

I am interested in finding the maximum temperature of the rotor an electric induction motor during normal operation. The problem is that the rotor is a rotating assembly within the closed assembly of the motor. We are currently testing using nonreversible temperature stick-on labels (through Omega Engineering Inc.), the type where a square/dot set for a certain temp. turns black once that temp. is reached. The problems is that the labels did not stay on for the first test (rotor spinning at 3600rpm, max temp somewhere over 100C). We tried using epoxy around the edge of the labels to keep them on, but this is troublesome to apply and may get underneath the temp. sensing dots and insulate them. Also some of the labels can be scraped off during assembly of the motor.

Therefore, my question is, does anyone know of a better method to measure the maximum temperature of a rotating body within a closed assembly (closed at least during operation of a full heat run test)?

Your assistance is appreciated.

 

[hacksaw]

Infrared sensors work great.

 

[JOM]

Is the end of the shaft exposed or encased in a bearing?

If exposed, could you place your tell tale labels there?

Infrared thermography? Can you run the motor, stop it and rapidly strip it down and get a sensor onto the shaft as quickly as possible?

I have some memory in the back of my mind where a similar problem occurs. I think it might be in measuring temperatures inside combustion chambers (engines? boilers?). I remember it involved plugs of solder of various melting points.

What about drilling a hole in the centre of the shaft and inserting a thermocouple? Could that be done and still run the motor? Cheers,
John.

 

[pmover]

An aside note:
be careful about removing or adding weight to a rotating piece of equipment as an imbalance may occur - especially at higher rpm's.
i've no idea how to measure temperature on a rotating piece of equipment other than obtaining the data when the rotor is not in motion. the sticky labels sounds good, perhaps you can contact Omega and request them to provide a method of adhering the labels without impacting the temperature results. you should provide the motor data (i.e. rpm and radius) to Omega to they can do some analysis work as well.
good luck.
-pmover

 

[daninacan]

The problem is that we want to know the overall maximum temp. within the motor. Therefore shaft temperatures won't work since the "hot spot" is the surface of the rotor (at least that will contact the air). It is impossible to disassemble the motor fast enough to get a true maximum temp. The rotor is concentric with the motor stator with only a few millimeters gap between the two. I don't believe we can drill through the stator to point an IR temp. sensor at the rotor, as least I'd like to avoid it if possible.

Are there any wireless thermocouple options? Or something we could embed in the rotor that would send a signal to a receiver outside the motor? I haven't had any luck finding anything like that. If we insert a thermocouple into the rotor there is nowhere for the wires to go without getting twisted around to the point they break off.

 

[ivymike]

how about using temp-plugs?

 

[JOM]

daninacan,

tiny wireless data tranceiving packages are used in medical applications; eg, programmable pacemakers, cochlear implant, there's a tiny video capturing device that transmits pictures to outside the body as it travels thru the patient's gut

so in theory, a wireless t/couple isn't as far fetched as it first seems; would the electrics of the motor play merry hell with its transmission? perhaps it could be a recording device rather than transmitting?

fusible solder plugs should work but where would the molten solder go?

can the heat sensitive chemical in the labels be painted on?

i'd suggest if you find a solution, slap a patent on it.
Cheers,
John.

 

[JOM]

is this line of thought useful?

you're searching for a way to wire in a temp sensing device (at least that's one approach0; you already have an electrical device inside the motor and already wired up to outside the motor - ie, the stator;

can the temp of the stator be measured by looking at the resistance of its windings - the ohmeter would be connected to the external terminals; any sense in that?

i realise you want the rotor's temp not the stator's, but it'd be a neat solution even if it doesn't solve your problem <grin> Cheers,
John.

 

[hacksaw]

The IR devices for motors and other closed devices are performed with a fiber optic probe. The sensor is located outside.

The fibers are quite small and easily routed inside your equipment.

They are considered a proven technology.