Anyone work with process control, specifically water temp?

[Kayos]

Oops!! Must be some fairly nasty stuff in there

I'm not sure, but 3 minutes at 37.8 deg and it turns a roll of film into 36 pictures

 

[Kayos]

if you get bored waiting for it to be delivered, I have a couple of spare PT100s. The probe is stainless but the cable strain relief is just chromed so they tend to go a rusty without a bit of oil if its like the one below.

I may take you up on that, as my new trainee found out today, patience isn't my strong point

 

[Kayos]

The thermal path forming the part of the control loop between heater and measuring point needs to have the different components proportioned correctly, else the system will oscillate horribly at one end of the scale or produce very poor and sluggish control at the other. Putting the PID controller's temperature sensor in the bottle, whilst heating the large tank that the bottle is in, is not a good idea, since the tank is likely to get very hot and then take a long time to cool, with the bottle temperature then continuing to rise well beyond the setpoint. If, on the other hand, the bottle was placed in a very small tank i.e. low thermal mass, you might get away with it. A 2kW heater in a 30 litre bath, with the sensor in the bath, and everything well-stirred, should work well and get the bath up to temperature in reasonable time - about 10 minutes for a 10 degree rise in temp.

Incidentally, I bought one of these: http://sansaire.com/ - said it was for cooking steak to perfection....

Essentially the overshoot is one of the problems I was having while measuring bath temp as well, this did happen last night (until the probe dissolved ) but I'm hoping the auto tune will correct for it, I'm not heating one bottle, it can be up to 8 depending on the process I'm doing.

Speed isn't a problem either, if it overshoots but cools and maintains the temp I'm happy, accuracy is what I'm after, without watching a thermometer for hours

 

[Kayos]

The first of my PT100s turned up today, despite being listed for measuring liquid temp they are not sealed, so will only work in a dry pocket

Cant be bothered with that so ive improvised until the proper ones turn up

Few quick tests and its way better than the thermistor one I was using, and waaaaaaaaaay better than the K type

 

[brewdexta]

I have several PT100 that are waterproof, PM your address and I'll post one.

Here's how I fixed mine to the hot liquor tank in my brewery. The thread on the ones I got are M8 so took a piece of 15mm brass rod, drilled it and tapped it M8, fitted the probe with a bit of PTFE then slipped the 15mm rod into a standard push fit tank connector although a compression one does the same job.

and inside the hot liquor tank

Cheers
Andy

 

[Kayos]

I have several PT100 that are waterproof, PM your address and I'll post one.

Here's how I fixed mine to the hot liquor tank in my brewery. The thread on the ones I got are M8 so took a piece of 15mm brass rod, drilled it and tapped it M8, fitted the probe with a bit of PTFE then slipped the 15mm rod into a standard push fit tank connector although a compression one does the same job.

View attachment 60949

and inside the hot liquor tank

View attachment 60950

Cheers
Andy

PM on its way in a min

The ones that landed today let water in between the probe and the threaded bit, so it just runs through
The attachment is a good idea, I just used a couple of M8 washers and 1/2" tap washers as mine is just a plastic tank, alltho I did use a similar method to yours with a 10mm bush to fit some cartridge heaters to a tank, with 15mm tank connectors

 

[brewdexta]

Mine are only waterproof south of the thread, not on the cable side, so could be the same as yours. NP sending it if you want to compare

 

[Kayos]

The probe landed today, once I've swapped the rad on my sisters stupid pointless automatic micra I will be giving it a go

Good timing too as my Russian cameras landed today, so I can finally play with some 120 film

 

[Kayos]

Final prototype finished, xlr connectors for the temp probes and a switch to choose between 2, either different heights in the tank or a bottle temp probe to see how it's doing

Final version will be in a metal case with the SSR inside as its in a 13 amp double socket at the min, with iec connectors for power in and power to the heater(s)

Big thanks to Brewdexta for sending me a probe that works below the water line

 

[voipio]

How's the project going? Are you pleased with the performance?

I once used a PID controller to keep the tip of a 0.2mm wire diameter thermocouple to within +/-0.01 degC by pointing a car headlamp bulb at it. The headlamp was powered by a simple current amplifier driven from the controllers output, which was analogue proportional in a 12V system. The thermocouple signal went through an Analog Devices thermocouple amplifier to the controller's DC input to give the 0.01degC resolution. Quite impressive. I could blow on the thermocouple to try to cool it and the bulb simply brightened. The temperature didn't go beyond 0.01degC from the set-point.

With the Sansaire device, it's possible to jam a tubing connector into the outlet hole and use the device as a circulator. Sitting in 2 litres of water, it gets up to 37degC in a couple of minutes and tends to under/overshoot by about 0.2 degC. In 10 litres, the temperature control stays within 0.1degC.

 

[Kayos]

I'm very happy with it so far, have used it at both 37.8 deg for colour and 20 deg for black and white film, no overshoot on the colour chems, which was an issue with the thermistor sensor.

I'm glad I added the second sensor with a switch, it takes a second or so to recover when switching but I like to be able to see the bottle temp with a flick of the switch and not having to squint at a thermometer, it also seems to heat the bottles quicker.

Once I've done a few more tests I will be sticking it in a metal case with iec (kettle) plugs/sockets for supply and for the heater supply, I may try the 2kw heater for comparison but with the SSR the aquarium heaters seem to be behaving now