Playing with a PID

In the process of building the electric kettle, I bought a PID (proportional-integral-derivative) controller to control the kettle temperature.  Since this came from Amazon and had Chinglish directions, I figured I should get it out of the box and test it.

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The Controller

The controller is a little 1.75″ x 1.75″ (45mm x 45mm) square.  The screen has two displays, one for the temperature, one for the set point. There are also four buttons, SET, <<AT, up, and down.

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Test Setup

I threw together a setup that has a switch (in this case, a double-pole switch built for 220V 45A), a plug, and the PID.

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Running in Centigrade

Initially, the PID is setup in Centigrade.  You can change it by holding down ‘set’ for a few seconds and then pressing it until you see a C F in the upper screen and using <<AT and up or down to change it from C to F.

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Switched to Fahrenheit

The output is 24 VDC.  There is also an alarm that is basically a switch (normally opened, closed during an alarm condition). The set includes some slip brackets (that’s probably not the proper name) to mount it in a box.

The issue I ran into with this is that the thermocouple is a less-common thread size – I don’t have the correct size nut and my tap set doesn’t have the correct size, either.  I did find the right size at the hardware store (a 6mm nut).

I also had to find the right locknut for the heating element.  Apparently, this is standardized to a 1″ nut, and they run less than $4 at Grainger.

Almost ready for drilling.

Almost ready for drilling

1 1/4" outside the threads

1 1/4″ outside the threads

1/4 inch outside the threads

1/4 inch outside the threads

So the next post should include something about getting this running in sort of a basic semi-usable and somewhat unsafe configuration.  I’m sure my 50 amp spa panel will be part of things, as well as the switch I used above, and the PID controller of course.  However, the PID controller won’t be controlling anything until I get the solid state relay.  That’s probably stuck in the harbor outside of Long Beach; fortunately it shipped a few weeks before the Chinese New Year, and you really only need a few days (if that) for it to leave China and not be affected by the holiday.  So the delay is all on Long Beach.

In the meantime, I ordered a pair of SSRs to be shipped from Georgia.  Which will probably arrive next Monday.