Heat and Prox switch

[ptonsparky]

We’ve had an non shielded proximity sensor detecting a key on a shaft for several months with no problem. Last week @ 102 degrees air temp it decided to stay ‘closed’. Got it loose and noticed it working again. Reinstalled it the next morning until I get a replacement and it has worked in the temps below 100. These are <$30 two wire DC units and even though the temp was below the 125 F upper limit I suspect temp was the issue. Yes/No/Maybe?

I will be trying a shielded unit this time because of the amount of surrounding metal. That caused us to set the original out to its max distance to miss the shaft vs the key.

 

[gadfly56]

I suppose 102°F might be tickling the upper limit of operation. Was that the ambient environment? Are there radiation sources that would boost the temperature locally? You could use a heat sensitive sticker or marker to confirm.

 

[ptonsparky]

I suppose 102°F might be tickling the upper limit of operation. Was that the ambient environment? Are there radiation sources that would boost the temperature locally? You could use a heat sensitive sticker or marker to confirm.

I didn’t do a thermal scan but I could comfortably touch the surrounding area.
Air temperature for the surrounding towns.

 

[gadfly56]

I didn’t do a thermal scan but I could comfortably touch the surrounding area.
Air temperature for the surrounding towns.

The "ouch!" point for contact with bare metal is about 140°F, but just a layer of paint can move that up. Maybe you have a sensor that is out of bounds on the low end of the high limit for proper operation. If you've ordered a replacement, you might want to consider getting a spare as well, since it's relatively low cost.

 

[petersonra]

We’ve had an non shielded proximity sensor detecting a key on a shaft for several months with no problem. Last week @ 102 degrees air temp it decided to stay ‘closed’. Got it loose and noticed it working again. Reinstalled it the next morning until I get a replacement and it has worked in the temps below 100. These are <$30 two wire DC units and even though the temp was below the 125 F upper limit I suspect temp was the issue. Yes/No/Maybe?

I will be trying a shielded unit this time because of the amount of surrounding metal. That caused us to set the original out to its max distance to miss the shaft vs the key.

It may be somewhat temperature sensitive. Inductive sensors usually have a temperature sensor built in to try and compensate for temperature differences but it may not be working perfectly.

 

[gar]

210623-2058 EDT

Everything in the universe is temperature sensitive. Different materials and designs have different sensitivities to temperature.

"The words eutectic solder describe a solder alloy that melts and freezes at one single temperature. A good example of this is Tin 63% / Lead 37% solder which meltsand freezes at 183 °C. This melting point is much lower than the melting points of either pure metal which are 232 °C (tin) and 327 °C (lead)."

Internally most electronic components have a problem before 100 deg C. Some may not be designed to work above an exterior temperature on the surface of the sensor above 40 C = 104 F, 50 C = 122 F, 60 C = 140 F, etc. Very few for an exterior temperature of 100 C.

It is quite possible the prox sensor is defective. Take it out of the machine and do some bench tests on the sensor vs temperature, applied voltage, and sensing gap distance. The simplest test is to see how it performs with nothing in proximity, and adjust voltage over its rated voltage range and see if it changes state. Then proceed to temperature and voltage tests with nothing in proximity. Next see if the mounting structure has an effect. Last you test for how range of sensing varies with different materials being sensed, and the voltage and temperature tests.

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[ptonsparky]

The "ouch!" point for contact with bare metal is about 140°F, but just a layer of paint can move that up. Maybe you have a sensor that is out of bounds on the low end of the high limit for proper operation. If you've ordered a replacement, you might want to consider getting a spare as well, since it's relatively low cost.

Ordered two.
I had thought I had a a spare unshielded, but nope.

 

[Jraef]

The ambient rating (assuming 125F is really 50C) is for surrounding air. If the surrounding air is 102F and this is mounted next to a motor that is radiating additional heat, the immediate area around that sensor may have easily exceeded 125F.