Not long to go now, the hard works pretty much done
Mark 1 controller for RIMS
Houston, we have lift-off. The element detector circuit didn't work because the op-amp chip was f***ed. With a new chip it works really well. It only took me three months to get the thing taken to work and show my friend. Everything looked OK but the op-amp didn't amp, so we put another chip in it and bingo!
Here is the second lash-up control box with three LED indicators:
and here is a rather blurry close-up:
showing the 12-volt power supply is OK (this is a switch-mode PSU from an old Lacie Jaz drive housing to power the current detector circuit); and at a moment when the PID is powering the element we get a Heating LED, fed from the 10V SSR output, and Element OK, fed from the current detector - no direct connection to the PID-SSR circuit!
I was getting very unreliable temperature readings when I tried to calibrate the PIDs against my usual digital thermometers - one was fine once I'd set some value in PSb, and the other never read the same twice running.
The digital thermometer and the two platinum resistance probes tied together:
and in the ice bath:
Eventually (on the brewing morning, Sunday 20th) I worked out that there must be a dodgy electrical connection in the one that was weird. When you turn on the PID, and every time you change the measured temperature offset (the PSb register), the PID re-calibrates itself according to what it finds on the thermocouple/thermometer input. The platinum resistance thermometer has three wires, one to one end of the resistance element in the tip, and two wires to the other end of the resistance. If one of the two reference wires doesn't conduct consistently then the temperature reading will keep changing in a crazy fashion when the PID recalibrates. (18 degrees, minus 14 degrees, 152 degrees...)
I re-made the solder joints in the plug on the end of the probe lead and the socket on the box, and soldered the crimp terminals which go onto the PID. Now I was getting reliable readings, so I could match the temperature of the mash liquor as it was heating up on both the PID and the digital thermometer. I only got it to within a degree and a half, but it was consistent throughout the range of brewing temperatures so I could do my temperature-stepped mash
Brewday pics and HERMS post now live.
Here is the second lash-up control box with three LED indicators:
and here is a rather blurry close-up:
showing the 12-volt power supply is OK (this is a switch-mode PSU from an old Lacie Jaz drive housing to power the current detector circuit); and at a moment when the PID is powering the element we get a Heating LED, fed from the 10V SSR output, and Element OK, fed from the current detector - no direct connection to the PID-SSR circuit!
I was getting very unreliable temperature readings when I tried to calibrate the PIDs against my usual digital thermometers - one was fine once I'd set some value in PSb, and the other never read the same twice running.
The digital thermometer and the two platinum resistance probes tied together:
and in the ice bath:
Eventually (on the brewing morning, Sunday 20th) I worked out that there must be a dodgy electrical connection in the one that was weird. When you turn on the PID, and every time you change the measured temperature offset (the PSb register), the PID re-calibrates itself according to what it finds on the thermocouple/thermometer input. The platinum resistance thermometer has three wires, one to one end of the resistance element in the tip, and two wires to the other end of the resistance. If one of the two reference wires doesn't conduct consistently then the temperature reading will keep changing in a crazy fashion when the PID recalibrates. (18 degrees, minus 14 degrees, 152 degrees...)
I re-made the solder joints in the plug on the end of the probe lead and the socket on the box, and soldered the crimp terminals which go onto the PID. Now I was getting reliable readings, so I could match the temperature of the mash liquor as it was heating up on both the PID and the digital thermometer. I only got it to within a degree and a half, but it was consistent throughout the range of brewing temperatures so I could do my temperature-stepped mash
Brewday pics and HERMS post now live.