PID Temperature Controller

AC_Hacker · 08-22-12, 05:07 PM

PID stands for proportional–integral–derivative and is a way to apply optimized feedback to reach a desired target, be it a temperature, volume, speed, or even an enemy naval vessel. It will maintain a temperature with great accuracy, too.

I found a really cheap one on ebay for about $25, free shipping, so I thought I'd investigate.

It took so long for it to arrive from China that I forgot that I had ordered it, but I still remembered that I wanted to get one and was about to order, when the package turned up in my mailbox.

The product and the enclosed document were all in Chinese, but there was the model number written on the controller: XMT7100

I looked through the Internet for a reasonable manual, found a lot of poorly written ones, but finally found a good one LOCATED HERE.

The controller needs voltage (110v to 220v) not only to work, but also to set it up for your application.

Here is a diagram in the manual which includes the 'pin out' (screw-out?):

I scrounged an old lamp cord & plug and connected to screws 1 & 2 (if you look at the screw area, there are numbers near each screw). I used small crimp-on spade connectors to avoid any nasty shocks.

Now the unit will light up and the menus can be investigated. When you push the SET button, the numbers will all turn to blinking zeros, the ">" button will let you step from number to number. The '^' button will let you increment the digit you are on, and the 'V' button will let you decrement the digit.

The codes to get you into the various menus are:

0089
0036
0001

To get into a particular menu,

push SET
use > to go to the digit you want to change
use ^ an V to set the digit
repeat for other digits if reqiired
press SET to enter the menu

Once in the menu, various choices are available to you, and each menu includes a choice called 'END' which allows you to exit a menu.

The diagram below, is in the manual and is supposed to explain all of this to you. Hopefully, between my description and the manual, you'll have no problem.

The controller will allow you to use an auto tune feature that will automatically go through a brief test cycle and set the optimum PID coefficients for best operation, based on the heat output of your heat source, and the thermal mass of your system. The auto tune function is initiated by pressing the '>' button for more than 3 seconds, at which time the small LED on the left side of the display begins rapidly blinking. When the test phase is complete, the LED returns to normal operation. So, if your heat source or the thermal mass of your system change appreciably you should run the auto tune feature again.

I sketched out a hasty wiring picture:

And wired it up to a small water heater to use as a Sous-vide egg cooking experiment. Again I used crimp-on insulated connectors:

After I ran the auto tune function, I put my egg in for one hour at 65 decrees C.

The controller will rapidly increase heat to the set point, not overshoot, and with brief pulses of electricity, hold the temperature dead on.

It will remember its settings when unplugged.

The controller has a built in relay (screws 4 & 5) that is designed to operate a visible or audible alarm if some set point is reached. That set point is programmable via the menu system. The set point can be established to be at the target temperature, at a higher temperature, or at a lower temperature. The relay, though designed as an over-temperature alarm, can be used for other interesting purposes, for instance some folks have used it to activate the water pump in an espresso machine, so other uses may come to mind.

The main output of the PID (screws 9 & 10) is a pulse of about 4 volts, low milliamps, of PID controlled variable-duration, that is designed to turn on and off a relay, or better yet, a solid state relay. In the early part of the warm-up cycle, the pulse is fairly long duration, as the controller approaches the target temperature, the pulse width begins to get shorter, and when the target temp is reached, very brief pulses precisely maintain the temperature.

If you get a PID controller, you'll likely want to get a solid state relay, too. I got a 25 A 220v SSR, from ebay for about 6 or 8 bucks, free postage. I bought four of them.

You'll also need a thermocouple. I already had some K type thermocouples laying about. My controller will also ten different types of thermocouples, so you'll need to carefully read the specs on the controller you choose. I'd say that a thermocouple with a three foot long cable would be better than the one that I have with a two foot cable.

BTW, of you plug the thermocouple leads in backwards, the temp readings will go down when they should be going up... just switch the leads.

Uses:

I got this controller to put in my espresso machine, because it's temperature controller went on vacation.
I can see that one would also be good to control a small annealing oven for treating steel.
a Sous_vide oven (they usually cost a bunch-o-bucks)
Also to control a kiln for ceramics.
Also an aquarium.
Also a refrigerator (my controller has cooling mode).
and many more...

It's a fist full of technology for $25.

Incidentally, the 65 degree egg was delicious.

-AC

08-22-12, 05:07 PM	#1
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 723 Times in 534 Posts	PID Temperature Controller PID stands for proportional–integral–derivative and is a way to apply optimized feedback to reach a desired target, be it a temperature, volume, speed, or even an enemy naval vessel. It will maintain a temperature with great accuracy, too. I found a really cheap one on ebay for about $25, free shipping, so I thought I'd investigate. It took so long for it to arrive from China that I forgot that I had ordered it, but I still remembered that I wanted to get one and was about to order, when the package turned up in my mailbox. The product and the enclosed document were all in Chinese, but there was the model number written on the controller: XMT7100 I looked through the Internet for a reasonable manual, found a lot of poorly written ones, but finally found a good one LOCATED HERE. The controller needs voltage (110v to 220v) not only to work, but also to set it up for your application. Here is a diagram in the manual which includes the 'pin out' (screw-out?): I scrounged an old lamp cord & plug and connected to screws 1 & 2 (if you look at the screw area, there are numbers near each screw). I used small crimp-on spade connectors to avoid any nasty shocks. Now the unit will light up and the menus can be investigated. When you push the SET button, the numbers will all turn to blinking zeros, the ">" button will let you step from number to number. The '^' button will let you increment the digit you are on, and the 'V' button will let you decrement the digit. The codes to get you into the various menus are: 0089 0036 0001 To get into a particular menu, push SET use > to go to the digit you want to change use ^ an V to set the digit repeat for other digits if reqiired press SET to enter the menu Once in the menu, various choices are available to you, and each menu includes a choice called 'END' which allows you to exit a menu. The diagram below, is in the manual and is supposed to explain all of this to you. Hopefully, between my description and the manual, you'll have no problem. The controller will allow you to use an auto tune feature that will automatically go through a brief test cycle and set the optimum PID coefficients for best operation, based on the heat output of your heat source, and the thermal mass of your system. The auto tune function is initiated by pressing the '>' button for more than 3 seconds, at which time the small LED on the left side of the display begins rapidly blinking. When the test phase is complete, the LED returns to normal operation. So, if your heat source or the thermal mass of your system change appreciably you should run the auto tune feature again. I sketched out a hasty wiring picture: And wired it up to a small water heater to use as a Sous-vide egg cooking experiment. Again I used crimp-on insulated connectors: After I ran the auto tune function, I put my egg in for one hour at 65 decrees C. The controller will rapidly increase heat to the set point, not overshoot, and with brief pulses of electricity, hold the temperature dead on. It will remember its settings when unplugged. The controller has a built in relay (screws 4 & 5) that is designed to operate a visible or audible alarm if some set point is reached. That set point is programmable via the menu system. The set point can be established to be at the target temperature, at a higher temperature, or at a lower temperature. The relay, though designed as an over-temperature alarm, can be used for other interesting purposes, for instance some folks have used it to activate the water pump in an espresso machine, so other uses may come to mind. The main output of the PID (screws 9 & 10) is a pulse of about 4 volts, low milliamps, of PID controlled variable-duration, that is designed to turn on and off a relay, or better yet, a solid state relay. In the early part of the warm-up cycle, the pulse is fairly long duration, as the controller approaches the target temperature, the pulse width begins to get shorter, and when the target temp is reached, very brief pulses precisely maintain the temperature. If you get a PID controller, you'll likely want to get a solid state relay, too. I got a 25 A 220v SSR, from ebay for about 6 or 8 bucks, free postage. I bought four of them. You'll also need a thermocouple. I already had some K type thermocouples laying about. My controller will also ten different types of thermocouples, so you'll need to carefully read the specs on the controller you choose. I'd say that a thermocouple with a three foot long cable would be better than the one that I have with a two foot cable. BTW, of you plug the thermocouple leads in backwards, the temp readings will go down when they should be going up... just switch the leads. Uses: I got this controller to put in my espresso machine, because it's temperature controller went on vacation. I can see that one would also be good to control a small annealing oven for treating steel. a Sous_vide oven (they usually cost a bunch-o-bucks) Also to control a kiln for ceramics. Also an aquarium. Also a refrigerator (my controller has cooling mode). and many more... It's a fist full of technology for $25. Incidentally, the 65 degree egg was delicious. -AC Attached Thumbnails __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker... Last edited by AC_Hacker; 08-22-12 at 08:53 PM..