Temperature probe identification

[ecclesk]

I need to identify the type of probe being used so i can replace a faulty thermostat, it is controlling one of three underfloor heating transformers for a large coldstore, the problem is that the system was installed in the mid 1970's and there is no clues as to the type of probe being used & also the probe i situated under the coldstore floor so changing the probe is not an option, it's a three wire (red, black, green) the thermostat is a Findlay Irvine dial type called a miniprobe electronic.

I have tried various types of thermostats, elliwells, dixells, lae for different probe types with no luck, i have been in touch with icefree who have done our more recent underfloor heating installations and they couldn't help.

I am pretty sure its not a PT100.

Readings taken with an ohm meter: red - green = 290.6

green - black = 288.4

black - red = inf

There must be some way of identifying the probe type?
Your help or advice greatly appriciated.

Thanks
Karl.

[chemi-cool]

Hi Karl

PTC and NPT probes got only two wires.
Dosen't leave you much, does it?

Chemi

[Peter_1]

In older instruments, they often used LM34 and LM35 sensors
Newer types are LM335: one pin is the ground - 2nd pin is power supply (4 to 15 VDC) and 3th pin is modulating voltage to instrument.(Fixed voltage proportional with temperature)
In the beginning were also thermistors used (KTY) but these have mostly 2 wires (the tirth wire is mostly, also with PT100 or PT 1000 for the subtraction of the wire resistance, mostly on long wires)

Try a Google ons this, I'm sure you will find something.

Post also here if you've found it.

Do also a search on MAX6612

[chillin out]

The only controller i have seen with 3 wires was on a freezer with a cascade system that went down to -80.
I can`t remember the case make, but when I was talking to the maint guy on site he had simalar probes spare in a box that were for ....?(Icant remember)

Why dont you measure the resistance of the probe and take a temp reading, then take say a dixell probe and do the same , now make the probes read the same by adding fixed resistors in line or paralell.
and / or calibrate the dixell?

[ecclesk]

Thanks for the advice people

i forgot to say earlier the temperarure that the readings were taken was aprox 0 to 10 degrees c, cant give an exact measurement as the thermostat/controller doesnt have a read out on it.

Try a Google ons this, I'm sure you will find something

Peter

manged to find some resistence tables for a few types of probes but none of them seem to match the type i have.

[ecclesk]

Ive spoken to the manufacturer and they faxed me an installation/set up manual (1976) but even that does not state the probe type, and no one i spoke to could advise me.

[Peter_1]

Can you post this fax here?

Chillin Out's proposal sounds also a good idea.
The heating of the underfloor is not a critical process.
What are the freezer dimensions and storage conditions?
Was there only one probe installed? If so, this was not such a good idea. We always install 3 probes and even removable afterwords.

[ecclesk]

Can you post this fax here?

Haven't got access to a scanner so i cant post it now will try later.

The heating of the underfloor is not a critical process.

I was always told it was crucial for large coldstores, to prevent frostheave. We had problems about 5 years ago with another cold store on this site (built mid 1960's) it had heated pumped glycol underfloor heating which seemed to be working ok but it cant have been circulating all the circuits as frost heave took over(12" rise in places) and we had to have the floor dug out, piles installed, new electric underfloor heating & then new floor, around £250,000 of work. I'll try to post some pictures later.

What are the freezer dimensions and storage conditions?

The coldstore in question is quite a lot bigger than the one discribed above and measures internally 45m x 45m x 8.5m heigh
both designed for -29c and always run at around -25c since installation

Was there only one probe installed? If so, this was not such a good idea. We always install 3 probes and even removable afterwords.

LowHeat, who installed many of these types of installations around this time in the UK and europe allways installed three probes, one for the thermostat and two for thermometers/displays. but even though LowHeat transformers were used this must have been installed by someone else?

The probes may well have been accessable on installation but since then the transformers & controlls have been moved and what was once a plant room is now an office, new walls put up where i think the probes go through to coldstore.


After speaking to various different people it looks like the only possible solution is to replace the probes

[Peter_1]

What I mean with critical is that as long as you stay above 0°C, everything is OK.

So you can do it also with a pulse/pause timer; say each day switching on the heaters 1/2 hr/night. But you don't have a feedback if this is enough.

We had a client with a froozen up floor which rose +/- 60 cm. I have pictures of it.

At another client, the original techs installed in the years 70 plastic evacuation tubes in the underfloor and they blow during the night in summer (2 hrs/night) warm surrouding air in it with a turbine. This for +/- 6 months/year.
The rest of the year it's shut-off.
They never had problems with it.

We mainly install underfloor heating with water/glycol, warmed by a HE and use the underfloor heating as some sort of a condenser.
One thermostat controls the system and another is used as an alarm thermostat.
A pressostat is installed on the water circuit to warn us of a leak.

[ecclesk]

We had a client with a froozen up floor which rose +/- 60 cm. I have pictures of it.

Can you post these some time, it would be interesting to see.

At another client, the original techs installed in the years 70 plastic evacuation tubes in the underfloor and they blow during the night in summer (2 hrs/night) warm surrouding air in it with a turbine. This for +/- 6 months/year.
The rest of the year it's shut-off.
They never had problems with it.

We have a similar set up at another of our sites, the coldstore is basically built on stilts so there is always air circulating under the floor.

[Peter_1]

You can see on the roof line which was straight in the beginning how the floor went up (picture with the Ter Beke Sign) (+/- 60 cm)
Freezer is +/- 12 x 15 m.
They did tests in the middle of teh freezer and the soil was frozen more than 4 m (!!) deep.

[chillin out]

Drill a hole in the floor and pray

[Peter_1]

A very good handbook in pdf for those who wants to know everything about temperature sensors
http://www.labfacility.co.uk/temperature_handbook.html

[ecclesk]

I'll try to post some pictures later.

See attached pictures.

Peter,

This coldstore is a totally different construction type to the one you show, the outside of the store is built using large reinforced concrete blocks (3.8m x 0.75m x 0.25m), then behind this inside the store are 12” thick polystyrene blocks which were covered in some sort of scrim cloth & plaster, some years back the whole store was lined with a more modern laminated panel for cosmetic & hygiene reasons.

What was the outcome of the Terbeke coldstore? Did it have to be taken down or is it still in use?


We were lucky with the coldstore shown in the pictures as the floor had been laid separately to the perimeter footings/foundations so the building remained intact it was only the floor which had risen.

A large hole had to be cut out of the side of the store to allow access for digging & piling equipment, all the wall panels had to be removed also.


Back to the original subject, It looks like the only solution is to replace the probes & controllers but accessing the probes is going to be a difficult task.

Thanks again for everyones help & advice on this mater,
I'll let you the outcome.

Karl

[Peter_1]

I was there for an article I have written in a small Belgium HVACR magazine.

Coolworld - a Dutch company - is renting there some large freezer containers while they rebuild the freezer completely.

The first thing they did was shutting it down so that the underfloor could start melting.
They will even remove the walls and floors.

Interesting anecdote: the responsible of Coolworld and Ter Beke explained me - he didn't knew I was in fact a tech and thought I was a journalist - how this could happen.
What I didn't told him was that we installed +/- 15 years ago all the cooling systems in that factory and I knew better then them hwhy the system failed.
We warned them in the past that this could happen once.
But I kept my mouth shut. It was fun on that moment.