PID Settings

[wv109323]

I just finished wiring up my Aubern PID and was testing it out. I have not hooked the output to the heating element yet. I was measuring the output voltage that will be going to the pot heating element. The PV was 82 degrees. The output voltage to the pot element was always at 120VAC even if I lowered the SV to below 82 degrees. Should not the PID turn off the element voltage once SV got below 82?
Is there a learning curve for the PID or was I doing something wrong?

[el34]

SSRs will leak a miniscule amount of current when in the OFF state but that's all your meter needs to measure 110V voltage. If your pot was plugged in that measured voltage would drop to zero.

Or maybe something's wrong and actually turning on your SSR. Can you measure the voltage at the input terminals? It (typically) needs to be between 3 and 32 volts DC to turn on the SSR.

Does your PID have its own little light that comes on when it wants the SSR on?

Also- a PID controller doesn't simply turn off if your SV is barely under the PV. For a good test lower your set value 10-20 deg under.

[wv109323]

Thanks EL34. I went back and checked everything. I found that I had the thermocouple polarity backwards for one thing. I thought I read that red was positive but yellow is positive.
I still read the 120VAC across the output at all times but I hooked up a 60W light bulb up and the PID controlled the load as it should but there was a time delay of 5-10 seconds. I was not anticipating the delay.
I hooked up the Lyman 20 lb. pot today and ran the lead temp. up to about 150 degrees F and everything seemed to work fine. I was not ready to get in a casting session until a day or two. I should be good to go then.

[dragon813gt]

The PID needs to learn before it will work properly. The P, I and D values are all adjustable. It should have a auto tune feature. Set the temp to 700, put it in auto tune and let it do it's thing. It's going to overshoot and undershoot the target temp until it dials itself in. It takes some time so don't plan on just setting the temp and go about casting.

[el34]

Hooking up a light bulb was a good idea. The 5-10 sec ON could have been just the PID doing its thing, which is part of the way it 'thinks'.

Does the PID's little OUTPUT ON indicator correspond with the 60W light? That'd tell you the SSR is behaving.

I have a neon light connected to my load output to show me AC power is being applied to the pot. If the pot isn't connected that lamp comes on even when the SSR is off and it's due to the teeny leakage current through the turned-off SSR. I'm about to hook up a high-value resistor across the pot output to eat the leakage current and my neon indicator will quit lying to me. I'll let you know what it takes, it'll prolly correct your meter.

[BACKTOSHOOTING]

Hooking up a light bulb was a good idea. The 5-10 sec ON could have been just the PID doing its thing, which is part of the way it 'thinks'.

Does the PID's little OUTPUT ON indicator correspond with the 60W light? That'd tell you the SSR is behaving.

I have a neon light connected to my load output to show me AC power is being applied to the pot. If the pot isn't connected that lamp comes on even when the SSR is off and it's due to the teeny leakage current through the turned-off SSR. I'm about to hook up a high-value resistor across the pot output to eat the leakage current and my neon indicator will quit lying to me. I'll let you know what it takes, it'll prolly correct your meter.

I have this problem also,
Sent you a PM, Steve

[el34]

Howdy Steve. I took apart my spankin' new Mypin PID to activate Alarm2 if I can figger it out. I want to use it for another front panel light. Somewhere over the weekend I might goof with the SSR leakage, the datasheet for one I have shows 1 mA max leakage in the off state. That's more than I expected but we'll find something easy. Just keep in mind that if you have the pot connected you won't read any output voltage when there isn't supposed to be any.

[wv109323]

EL34..Thanks for all the help. Now that I Have cast with the PID three times I really like it. I got to thinking that I was "messing with" the PID when I first hooked wired it an did not hook a load up to it.. I was switching the SSR on and the output was not hooked to anything. There was no way that the PID could learn when it should switch on and off because when it switched on there was no change at the thermocouple.
Anyway the first time I used it the variance was -5 and + 14 degrees at a set value of 700. Next time was -5 and +10. The third time was + or - 5.
It really helps in casting good bullets. Before I had a questionable thermostat. I would first cast a lot of rejects ,some good bullets, and then some frosted bullets. Now I can cast very few rejects and a whole lot of good bullets with none of them frosted. If I see and edge of the bullet starting to frost I can cast a little slower and correct the problem. Another thing is when adding lead to the mix you can let the lead get back up to the correct temp. The PID has shown me that I was not waiting long enough for the temp to recover when I added lead.
A hot plate to pre-heat your molds and a PID controller really ...really helps.

[el34]

Congrats wv, that rocks.

If you're still concerned about reading voltage on the pot output when the SSR is off I might be able to help.