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.

 

[Knobhead]

What a load of codswallop

 

[stevethesparks]

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.

Resistance increases with temperature!

 

[Farmelectrics]

were or who told you this golfpaul

 

[telectrix]

paul. measure the resistance of a 100watt light bulb ( cold ). it will be about 60 ohms. when hot the resistance is R =V/I. i.e. 530ohms.

 

[Simonslimline]

Maybe have a read about Superconductors as well.

 

[Besoeker]

What a load of codswallop

Don't insult the cod!

 

[Besoeker]

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.

A little personal experience that runs counter your assertion.
We do a fair bit of work in paper mills. They can be quite steamy - and I don't mean in the night club sense. Paper mills use a lot of water so humidity is high.

Typically, they have an annual two week summer shut where they maintain what needs to be maintained - then spend the next two months sorting out the new problems introduced.

I was at the start up of one in Scotland doing a few checks. The drive motors were DC and I was checking the insulation of a motor at the "wet end". The field winding was down to 50kohm to earth.
"Jimmy, I think we have a wee problem with this yin."
"Och, dinnae bother wi' it. A bit of heat is aw it needs."
"OK. You're the customer, pal."

So I energised the field and left it overnight. And, sure enough, it was up to 4Mohm by the next morning. This, I reported to Jimmy.

"Aye. Braw job. Braw job."

 

[Spoon]

What a load of codswallop

Say what you mean Tony.... Don't sit on the fence...

 

[Silly Sausage]

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.

Stick to PAT testing mate!!!

 

[Lucien Nunes]

Electrical resistance has an inverse exponential relationship with temperature

You missed out a crucial bit of information: In what material? Not metals, for example, as the above replies have pointed out.

 

[Silly Sausage]

You missed out a crucial bit of information: In what material? Not metals, for example, as the above replies have pointed out.

Interesting; Carbon, Silicon and Germanium have a negative temperature coefficient of resistance.

I never knew that!

 

[HappyHippyDad]

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!

 

[Knobhead]

A little personal experience that runs counter your assertion.
We do a fair bit of work in paper mills. They can be quite steamy - and I don't mean in the night club sense. Paper mills use a lot of water so humidity is high.

Typically, they have an annual two week summer shut where they maintain what needs to be maintained - then spend the next two months sorting out the new problems introduced.

I was at the start up of one in Scotland doing a few checks. The drive motors were DC and I was checking the insulation of a motor at the "wet end". The field winding was down to 50kohm to earth.
"Jimmy, I think we have a wee problem with this yin."
"Och, dinnae bother wi' it. A bit of heat is aw it needs."
"OK. You're the customer, pal."

So I energised the field and left it overnight. And, sure enough, it was up to 4Mohm by the next morning. This, I reported to Jimmy.

"Aye. Braw job. Braw job."

One of the reasons some AC motors have DC applied to the stator when stopped.

 

[Knobhead]

What a load of codswallop

From the OED

[h=1]Definition of codswallop in English:[/h][h=3]noun [/h][mass noun] British informal
Nonsense: I think that’s a right load of old codswallop
More example sentences

• Is it a spiritually enriching pursuit or load of old codswallop?
• We could have been giving him a load of old codswallop.
• That's actually a load of old codswallop - the Belgians brew the best beer in the world.

[h=3]Origin[/h]1960s: perhaps named after Hiram Codd, who invented a bottle for fizzy drinks (1875); the derivation remains unconfirmed.

 

[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...