Well, i never knew that

[golfpaul]

Electrical resistance has an inverse exponential relationship with temperature, i.e. as temperature increases, resistance will decrease and vice versa. Since the minimum acceptable IR test values are based on a fixed reference temperature (usually 20oC), the measured IR test values must be corrected to the reference temperature in order to make sense of them.



As a rule of thumb, the resistance halves for every 10oC increase in temperature (and vice versa). S if the measured IR test value was 2MΩ at 20oC, then it would be 1MΩ at 30oC or 4MΩ at 10oC.

 

[dingledong]

I thought germanium was something that grew in the garden

 

[telectrix]

I thought germanium was something that grew in the garden

rodney, you plonker!

 

[ian.settle1]

I thought germanium was something that grew in the garden

Thats a geranium you pillock

 

[telectrix]

can't blame him. silicons grow in silicon valley, bulbs grow in anything, cannabis grows in attics,

 

[Besoeker]

rodney, you plonker!

I think he was pulling yours........

 

[BroadReach]

Threads like this is why I really love reading this forum

Makes me smile!!

 

[Brightspark2]

What I struggle to understand is temperatures link to speed....

When's it hot I go slow, when it's cold I go even slower because I can't get out the van...only when it is just right (according to my internal thermonitor) can I work...its a strange one...

 

[Spoon]

..only when it is just right (according to my internal thermonitor) can I work...its a strange one...

Is that how far your danglies are dangling down?

 

[Brightspark2]

Is that how far your danglies are dangling down?

ha ha wahey, thats the one!!!...

 

[Deleted member 72666]

Electrical resistance has an inverse exponential relationship with temperature, i.e. as temperature increases, resistance will decrease and vice versa. Since the minimum acceptable IR test values are based on a fixed reference temperature (usually 20oC), the measured IR test values must be corrected to the reference temperature in order to make sense of them.



As a rule of thumb, the resistance halves for every 10oC increase in temperature (and vice versa). S if the measured IR test value was 2MΩ at 20oC, then it would be 1MΩ at 30oC or 4MΩ at 10oC.

Ahh! That explains why we've just had a brownout, it's 35 degrees in Cyprus at the mo, dead short all round me thinks lol!

 

[Besoeker]

It looks like 'most' ceramics have a NTC as well!! Probably not that related to electrics but interesting as I thought temperature always had a positive coefficient with respect to resistance!

You can get PTC and NTC thermistors.

A while ago I did a bit of work for another division of our company on NTC thermistor assemblies.
Many here may be familiar with these for motor winding temperature monitoring for protection - simple, the thermistor is fed into a thermistor relay with contacts in the stop circuit.

This was a bit different. A medical application for monitoring liquid anesthetic to ensure that it didn't drop below a certain level.
The thermistor was powered and as long as it was in the liquid it stayed cool. The voltage across it was monitored by a voltage sensing circuit. If the liquid level fell, the NTC got hot and the lower voltage triggered an alarm.

Unfortunately, the original supplier of the actual thermistor beads decided not to make any more so we had to cast around for an alternative. It was proving very difficult/impossible to get the same characteristics and I was asked to look into it. I did - if I knew then.....

Anyway, others had been trying to replicate the original NTC characteristic with no success so I took a different tack. What actually does it do? Switches a voltage detector so all I needed was to get two switching points the same which I did with a different thermistor. Job's done and a good 'un...........

Except it wasn't. The customer had to get the change past the FDA - US client.
A whole new can of worms. I didn't know whether to laugh, stab somebody, or get my wife to give me forty lashes with the cat-o-nine tails. I decided on the latter......

We, that is me, had to write a War and Peace tome that included a 100 page document on FMEA - failure mode and effects analysis.....for a TWO wire device FFS!.......Not applicable combined with copy and paste are my friends.

This is a cautionary tale.
Messing with medical is not for the faint hearted.
You're more likely to become a customer than a supplier.

 

[golfpaul]

Stick to PAT testing mate!!!

Now, now...