This is a look into how I use a PID controller as a temperature gauge and alarm for my transmission.
Automotive temperature gauges, even expensive ones are normally pretty poor at low temperatures if they even work at all. PID controllers take a variety of high quality sensors that work over a wide range of temperatures. They can make an affordable alternative to standard automotive gauges. Because they are primarily designed as controllers it is easy to add a temperature alarm. You can use almost any temperature sensor, I use a platinum three wire sensor or Pt100. Although I use it on my transmission you could just as easily use it for EGTs or anything else, they are pretty flexible.
The controller I use is called an XMT 7100. I ordered one similar to this for about $20. It's important to get a 12V version. You can pick the LED display color and relay or SSR control. I use the relay version with white LEDs. For a temperature sensor, as I mentioned, I use a Pt100 sensor. It is a very good temperature sensor type, lab quality. Mine is 1/8 BSPT, unfortunately they are often labeled overseas as 3/8-24 or 1/8 NPT so it can be difficult to get the correct senor. They can be found for well under $20. They are a bit more expensive with NPT threads.
The one I use is labeled PT 1/8", not very helpful. You should order the correct length wires, if you do splice the wires it's important to keep all three extensions the same length and type of wire. I found 1m was just enough but it's very close.
I used a 1/8 BSPT tap to thread my transmission pan. If you have a standard pan you'll probably attach a threaded bung. These sensors have longer probes than some others I've seen so you have to take care where you mount them so it clears the internal transmission parts. You can also use any standard sensor with the PID controller like a normal resistor or K type. If you want a 1/8 NPT Pt100 sensor I think they are available from Auber Instruments at a reasonable cost.
The controller uses power from my accessory circuit. I mounted it in the space where the 2004 cigarette lighter socket is. It appears that Jeep sized the area for each socket just about 1/32 DIN so it's a good fit. There is a bit of overhang where the socket was so I used a small gasket on the front side and hot glue along with the clips to secure it from the back. The alarm is a simple 12V beeper I picked up from a local surplus store and is connected through the controllers relay output. You can use the relay output for an indicator light or anything really.
The wiring isn't too complicated and all fits with a little trimming of the dash support plastic behind the front panel. The controller is a bit long but there's nothing really in the way behind it after a little trimming. I attached the beeper on top of the controller with a dab of hot glue so it doesn't rattle around.
Once everything is installed you have to setup the controller. This is a bit complicated, you press "set" and enter the pass code 0089 into the controller and go though the basic setup items. For simple use the first two items are the only important settings:
inty = PT10.0 (you can also us PT100 if you don't want the decimal)
Outy = 4 (simple relay output at set value)
Once you get those set you cycle through to the end and exit the setup menu. All the other parameters aren't used, they are for the more complicated PID functions. To set the alarm set value or SV on the controller you use the up and down arrows. It's helpful to bring the SV down and trigger the alarm at the current temperature to test the relay and alarm. If you've got it setup correctly the indicator light will also turn on when you reach the SV threshold. You can also enter a menu for that entering the code 0001 but since the arrows set temperature there's not much point in going into that menu. You can set all types of delay and hysteresis functions but out of the box it should work okay.
The brightness on the display does not dim and it is bright. Fortunately for me it is out of view in my normal driving position. That may seem strange but I can lean over a bit to read the display and it isn't distracting at night. It works well to illuminate my console area and the alarm is enough to let me know if I need to check it. If you decide to mount it where it is always in view it might be too bright at night. I initially had it on a toggle switch without the beeper but when I added the alarm beeper I wired it on all the time. I found I never turned it off anyway.
I set my temperature alarm at 225F, the 42RLE changes to overheat shift schedule at 240F.
@NashvilleTJ and @hear asked for some details about this but it's been awhile since I did the whole thing. If I left out some important bits or if anybody has any questions obviously let me know.
Automotive temperature gauges, even expensive ones are normally pretty poor at low temperatures if they even work at all. PID controllers take a variety of high quality sensors that work over a wide range of temperatures. They can make an affordable alternative to standard automotive gauges. Because they are primarily designed as controllers it is easy to add a temperature alarm. You can use almost any temperature sensor, I use a platinum three wire sensor or Pt100. Although I use it on my transmission you could just as easily use it for EGTs or anything else, they are pretty flexible.
The controller I use is called an XMT 7100. I ordered one similar to this for about $20. It's important to get a 12V version. You can pick the LED display color and relay or SSR control. I use the relay version with white LEDs. For a temperature sensor, as I mentioned, I use a Pt100 sensor. It is a very good temperature sensor type, lab quality. Mine is 1/8 BSPT, unfortunately they are often labeled overseas as 3/8-24 or 1/8 NPT so it can be difficult to get the correct senor. They can be found for well under $20. They are a bit more expensive with NPT threads.
The one I use is labeled PT 1/8", not very helpful. You should order the correct length wires, if you do splice the wires it's important to keep all three extensions the same length and type of wire. I found 1m was just enough but it's very close.
I used a 1/8 BSPT tap to thread my transmission pan. If you have a standard pan you'll probably attach a threaded bung. These sensors have longer probes than some others I've seen so you have to take care where you mount them so it clears the internal transmission parts. You can also use any standard sensor with the PID controller like a normal resistor or K type. If you want a 1/8 NPT Pt100 sensor I think they are available from Auber Instruments at a reasonable cost.
The controller uses power from my accessory circuit. I mounted it in the space where the 2004 cigarette lighter socket is. It appears that Jeep sized the area for each socket just about 1/32 DIN so it's a good fit. There is a bit of overhang where the socket was so I used a small gasket on the front side and hot glue along with the clips to secure it from the back. The alarm is a simple 12V beeper I picked up from a local surplus store and is connected through the controllers relay output. You can use the relay output for an indicator light or anything really.
The wiring isn't too complicated and all fits with a little trimming of the dash support plastic behind the front panel. The controller is a bit long but there's nothing really in the way behind it after a little trimming. I attached the beeper on top of the controller with a dab of hot glue so it doesn't rattle around.
Once everything is installed you have to setup the controller. This is a bit complicated, you press "set" and enter the pass code 0089 into the controller and go though the basic setup items. For simple use the first two items are the only important settings:
inty = PT10.0 (you can also us PT100 if you don't want the decimal)
Outy = 4 (simple relay output at set value)
Once you get those set you cycle through to the end and exit the setup menu. All the other parameters aren't used, they are for the more complicated PID functions. To set the alarm set value or SV on the controller you use the up and down arrows. It's helpful to bring the SV down and trigger the alarm at the current temperature to test the relay and alarm. If you've got it setup correctly the indicator light will also turn on when you reach the SV threshold. You can also enter a menu for that entering the code 0001 but since the arrows set temperature there's not much point in going into that menu. You can set all types of delay and hysteresis functions but out of the box it should work okay.
The brightness on the display does not dim and it is bright. Fortunately for me it is out of view in my normal driving position. That may seem strange but I can lean over a bit to read the display and it isn't distracting at night. It works well to illuminate my console area and the alarm is enough to let me know if I need to check it. If you decide to mount it where it is always in view it might be too bright at night. I initially had it on a toggle switch without the beeper but when I added the alarm beeper I wired it on all the time. I found I never turned it off anyway.
I set my temperature alarm at 225F, the 42RLE changes to overheat shift schedule at 240F.
@NashvilleTJ and @hear asked for some details about this but it's been awhile since I did the whole thing. If I left out some important bits or if anybody has any questions obviously let me know.
