PID build questions

Coffeeuk · Post by **Coffeeuk** » Wed Jan 21, 2015 2:25 pm

Hi,

I'm just getting the parts together for a PID to control my HLT. I have a few questions.

I'm using a metal cabinet, is it a good idea to ground it ? Is it just a case of running a wire from the power in ground to the box ?

If I want to wire in an led to let me know the Element is being powered, what's the best way to wire it in ?

I want to make the probe detachable, it's a PT100, what do people use to achieve this ?

Thanks in advance

Mick

LeeH · Post by **LeeH** » Wed Jan 21, 2015 2:32 pm

Coffeeuk wrote:Hi,

I'm just getting the parts together for a PID to control my HLT. I have a few questions.

I'm using a metal cabinet, is it a good idea to ground it ? Is it just a case of running a wire from the power in ground to the box ?

If I want to wire in an led to let me know the Element is being powered, what's the best way to wire it in ?

I want to make the probe detachable, it's a PT100, what do people use to achieve this ?

Thanks in advance

Mick

Yes, ground the enclosure

Put the LED in parallel with the output SSR terminals of the controller.

Use a thermowell if you want to detach the probe. Or any plug and socket arrangement if you don't.

Coffeeuk · Post by **Coffeeuk** » Wed Jan 21, 2015 2:51 pm

Cheers for the reply

I've got a thermowell, I meant at the cabinet end, what type of plug/socket do people use in the box ?

LeeH · Post by **LeeH** » Wed Jan 21, 2015 2:54 pm

Cheapest option is a 3.5mm jack plug, the headphone type ones from Maplin.

AnthonyUK · Post by **AnthonyUK** » Wed Jan 21, 2015 3:30 pm

Mini XLRs are also popular for PT100 especially the 3 wire versions.

The PID should display when it is active so no additional LED is really necessary

Coffeeuk · Post by **Coffeeuk** » Wed Jan 21, 2015 4:30 pm

AnthonyUK wrote:Mini XLRs are also popular for PT100 especially the 3 wire versions.

The PID should display when it is active so no additional LED is really necessary

The mini xlr is exactly what I was looking for. Added to my parts list

Cheers

Fil · Post by **Fil** » Wed Jan 21, 2015 5:24 pm

a simple 2ndary indicator is a 240v neon lamp connecting the ssr live output, and the element neutral feed, its also a useful indicator to have as an ssr can bleed a lil power when plugged in but not switched to active..

http://www.ebay.co.uk/itm/9mm-240v-Main ... 43c5bc6f9f for example

it was fitting one of these lamps inline that brought this ssr feature to my attention, if ignored and connected to your hlt when dry its possible to heat up the element unexpectedly all be it a lot slower than if the full mains load was bleeding through, but could still be a hazard.

LeeH · Post by **LeeH** » Wed Jan 21, 2015 5:27 pm

Forgot to say you need a 24VDC led if you are use my suggestion.

Fils will be a cheaper alternative I think.

Coffeeuk · Post by **Coffeeuk** » Wed Jan 21, 2015 6:42 pm

Will these be OK ?

http://pages.ebay.com/link/?nav=item.vi ... 1419615190

LeeH · Post by **LeeH** » Thu Jan 22, 2015 2:37 pm

For connecting in parallel across the heating element then yes.

For the SSR output....

http://pages.ebay.com/link/?nav=item.vi ... 1359006172

Coffeeuk · Post by **Coffeeuk** » Thu Jan 22, 2015 6:10 pm

Thankyou everyone for your replies, just waiting for all the parts to arrive now.

Post by **orlando** » Thu Jan 22, 2015 6:35 pm

A more fundamental question is why do you want this level of accuracy for an HLT? It's overkill, far better to use an STC 1000 for that job and reserve the PID for a RIMS/HERMS set up if you don't have one already.

Coffeeuk · Post by **Coffeeuk** » Thu Jan 22, 2015 8:30 pm

orlando wrote:A more fundamental question is why do you want this level of accuracy for an HLT? It's overkill, far better to use an STC 1000 for that job and reserve the PID for a RIMS/HERMS set up if you don't have one already.

It's part of my new Herms system. I'm running a copper cool through the HLT

Post by **orlando** » Fri Jan 23, 2015 8:11 am

Coffeeuk wrote:
orlando wrote:A more fundamental question is why do you want this level of accuracy for an HLT? It's overkill, far better to use an STC 1000 for that job and reserve the PID for a RIMS/HERMS set up if you don't have one already.
It's part of my new Herms system. I'm running a copper cool through the HLT

Phew, that makes sense. But I would go for RIMS.

LeeH · Post by **LeeH** » Fri Jan 23, 2015 10:50 am

I went RIMS at the last minute. It just seemed a neater solution to me.

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