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Thought this may help someone else out there.
I was fed up of switching on and off power to my heating blanket to control temerature, or playing with a router controller (which kept failing) so..
Bought a PID system, cheap

REX-C100FK02-V*AN, with 40A SSR + Heat Sink + 1M K type thermocouple probe

I bought mine from ebay uk, about $20 delivered, but these seem to be widely available internationally.
http://www.ebay.co.uk/itm/131752134751?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
110/240V input so "international" voltage.
Box as delivered says brand RKC, Japan, and item says BERME Manufacturer, made in China, so may be a knock off? - Came with manual, in Chinese....... But manuals available in English on the net.
Problem was, I'm not much of an electronics geek at all.
Electrics OK, I can an change a light bulb and wire a plug, maybe even read a circuit diagram if it's not got too many symbols in it, but not a whole lot more.
Found several wiring diagrams on the net, none the same.
WTH, only cost $20 and I had a fire extinguisher on hand.
Picked a couple of the simpler ones, and tried them. Second one worked (and no melt down)
The wiring diagram which worked for me is underneath -
(Note the model number in the diagram is slightly different to my model, but, details, details....)



The thermocouple was much too big to fit in between slats, so I just opened it up carefully, and threw away the probe casing itself and found a small bead welding 2 wires together – stripped the insulation back about 1.5 cm, twisted the wire and tapped it a bit flat., and folded it back on itself in a semicircle.
Then sandwitched the exposed wire end in a square folded piece of alu foil, finally dimensions about 2.2 mm thick and 1.3 cm square.
Placed this alongside the side, seemed the best place, and the thickness was nicely gripped between the slats.

Switch on, press "set", cycle through the 4 flashing numbers (starts from RHS) using the "<" button, press up and down to change set temperature on lower display, press "set" again to enter new setting. Process temperature is shown on top. Not found out how to change it from deg C to deg F yet, the instructions for this in the manual don't seem to work for me (yet), yet another reason it may be a knock-off.

I tested everything first using first a lamp, then a kettle with the thermocouple sitting in the spout.

It has now been used in anger (with a separate proven digital thermometer to check) and worked well. Only thing was when dropping the temperature, it was better just to disconnect the heat blanket plug as the heater cut in and out as it approached the new lower set temperature. If this continues too long, controller once seemed to go into an alarm/cut off mode, to freeze up and stop supplying power - just unplug or switch off, and back on again - set temperature is retained and goes back to working again.

(Disclaimer – use at your own risk, consult an "expert" if you are hesitant)

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I bought 2 of these and they worked OK for a short time. I used one to control lamps under, or inside the mould, and the other to control a blanket outside. I also fitted high current relays to switch the lamps 500W and heater 1100W. The keyboards on both has bad switch damping so they take a bit of fiddling to set.
After a while they both began intermittent switching then stopped working and I abandoned them. I showed the setup to an electrical supplier who told me they were faulty reworks hence the low price? But he wanted me to spend much more.
After reading your post I tested them today and they seem to work again? With the relays I can hear the switching as well as see the ON green led.
The display units can be changed by going into SETUP mode.
Press SET for 5 sec then press SET until SL2 appears in upper display. The lower display will read 0000 for °C, change it to read 0001 °F. Then press set for 5 seconds to exit setup