Slip Ring Thermistor

[solocam92]

Has anyone connected a thermistor to a slip ring? I initially tried using a thermocouple but since there is a change in metals going through the slip ring unwanted emf voltages were generated which were dependent upon ambient air. My next thoughts were to try a thermistor or RTD and Wheatstone Bridge. If anyone has done this before and could lend some advice that would be great.

 

[btrueblood]

What temperature are you trying to measure? If possible, I would pass an amplified signal (i.e. volts, not millivolts) through a slip ring, due to the inherent noise generated by the rings. That is possible if you use solid-state temp. sensors (google LM34, through there are hundreds of similar components). Alternatively, put the amplifier for the thermocouple, rtd, or other low-voltage device on the rotating equipment, and pass power and and the amplified high-voltage signals across the ring. Third alternative, is put a battery powered radio device on the rotating component, and a receiver somewhere nearby...

 

[solocam92]

What do you mean by "what temperature are you trying to measure"? If your wondering degrees it would be between 20 and 120 degrees Celsius.

Thanks for the advice about amplifying the signal, I will look into it. Due to space constraints there would not be room to place a battery powered device anywhere on the rotating device. It is inside of a fractional horsepower electric motor.

 

[gruntguru]

Fourth alternative is 4 slip rings. Feed (and measure) the RTD or TC current through 2 of them and measure RTD or TC voltage drop using the other 2.

Engineering is the art of creating things you need, from things you can get.

 

[MikeHalloran]

There might be room to squeeze a small rotary transformer into your motor. It could carry power inbound, and buffered signals outbound, with no sliding contacts.





Mike Halloran
Pembroke Pines, FL, USA

 

[solocam92]

Thanks for the help guys. I will look into a rotary transformer but if it doesn't work try an thermistor with a possible amplifier.

 

[sreid]

How about infra red temperature measurement?

 

[solocam92]

Tried that and found the surface was too shiny to get a good infrared reading.

 

[hacksaw]

"found the surface was too shiny to get a good infrared reading"...

I suggest that you readup on the basics of IR temperature measurement.

 

[solocam92]

""found the surface was too shiny to get a good infrared reading"...

I suggest that you readup on the basics of IR temperature measurement."

What are you suggesting is wrong with that statement?

 

[IRstuff]

One option to the shiny surface problem is to paint a section with ultra-flat black paint. That's basically how copper headers are turned into blackbodies

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[solocam92]

The brushes of the motor (PM DC) contact the commutator where I am looking to measure so I can't cover/paint the surface. I tried painting a thin strip on the edge where the brushes don't contact but it was too small of an area.

 

[hacksaw]

Basically, you correct for the emissivity. Black body radiation is not manditory, but given that you do have a difficult measurment, you can expect to spend time and money to make a traceable measurement.

 

[solocam92]

Thanks for the clarification. I did run across that somewhere along the way but it didn't seem cost effective for what we were going for. I'd like to stay under a couple hundred dollars max for the equipment. I did not spend much time at all looking into it though. Do you know what kind of cost difference it would make?

 

[hacksaw]

You measurement requirements are so generalized as defy any specific answers.
For example,

1. Basis or evidence for even requiring measurement of the temperature real time.
2. Temperature range and accuracy requirements.
3. Response time requirements.
4. Applied voltages (to the slip ring) relative to ground or neutral.
5. Space limitations.
6. Atmosphere (air, inert gas, etc.)
7. Time frame in which you need to resolve your measurement design, and test, etc.
8. Traceability requirements (NIST, or some other agency).
9. Physical design of the slip rings and layout, etc.

Without addressing such issues, you can only expect the sort of answers you might expect at you local garden club.