Electronic Otterstat

[Bitsyncmaster]

Sensor in cooking oil test. These reading were taken as the temp dropped. The gauge seems to have some damping of needle moment. This was done with engine running to have the same voltage and ground drops over the circuit.

260 deg. on gauge = 249 deg. F on sensor
7/8 deg. on gauge = 232 deg. F on sensor
3/4 deg. on gauge = 220 deg. F on sensor
5/8 deg. on gauge = 211 deg. F on sensor
220 deg. on gauge = 200 deg. F on sensor
3/8 deg. on gauge = 188 deg. F on sensor
1/4 deg. on gauge = 175 deg. F on sensor

So assuming my thermostat opens around 190 that tells me the sensor I used for testing is different or something is faulty with my testing. Of course it could be my thermostat is faulty or someone stuck in the wrong thermostat. Also my fans kick on with the otterstat a little below the 3/8 gauge mark so that says the otterstat kicks on about 185 deg.

I'm assuming the gauge is a calibrated instrument since there is a calibration resistor on the gauge terminals. Maybe they did a crappy job calibrating or did the calibration for full scale. I would have done calibration at the 220 mark (half scale).

[DMC5180]

Which reading represents the middle White line?


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[Bitsyncmaster]

Which reading represents the middle White line?


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The 1/4 "deg." is the middle white line. That is where my gauge normally shows when driving.

[Bitsyncmaster]

I going to run another absolute temp test (real sensor temp to gauge reading). But I'm going to high temp epoxy my meter thermocouple directly onto the sensor. I'm thinking the oil temp is a little different than what the sensor reads. My meter sensor is about 1 inch away from the gauge sensor.

I'm not using that absolute value for any calibration in my unit, just want to know the accuracy of the OEM system.

I'm basing my calibration from the gauge readings. This is where my first idea of a new temp sensor installed in the coolant line would have been better but make installation harder.

[Bitsyncmaster]

Well I pulled the sensor from my pan of oil and found the ground wire lug was very loose. I had four nylon stand offs and the ground wire was attached to the screw holding the standoff. I guess the high heat or the oil did something to the stand off to make the nut get loose. So that may have affected my test.

Anyway, I glued the meter sensor (K type thermal couple) to the gauge sensor with high temp epoxy. I will add a dedicated screw to hold the ground lug on my aluminum plate.

[Bitsyncmaster]

I did a new absolute temperature check. Not any big change.

260 deg. on gauge = 243 deg. F on sensor
7/8 deg. on gauge = 234 deg. F on sensor
3/4 deg. on gauge = 224 deg. F on sensor
5/8 deg. on gauge = 213 deg. F on sensor
220 deg. on gauge = 204 deg. F on sensor
3/8 deg. on gauge = 192 deg. F on sensor
1/4 deg. on gauge = 177 deg. F on sensor

This test was also done heating the oil to 270 deg. F and letting it cool down until the gauge hit each mark. I do that because the oil temperature change rate is pretty slow. The gauge drives the sensor though one coil of wire in the gauge. I tested that coil resistance cold at 54 ohms. But at high sensor temps, the current flow is about 100 ma. so that may be heating the gauge and maybe affecting accuracy. I'm going to see if the values change starting cold and increasing the oil temp.

[Bitsyncmaster]

Ran the new absolute temperature test starting cold and slowly heating the sensor by turning the hot plate on and off for very short times. Hence the change in temps was much slower. I still think there is a little heating of the gauge causing a little calibration change when testing hot to cold. Also air temp was cooler this morning at 77 deg. F.

These values look more accurate for gauge calibration.

260 deg. on gauge = 254 deg. F on sensor
7/8 deg. on gauge = 244 deg. F on sensor
3/4 deg. on gauge = 233 deg. F on sensor
5/8 deg. on gauge = 223 deg. F on sensor
220 deg. on gauge = 213 deg. F on sensor
3/8 deg. on gauge = 200 deg. F on sensor
1/4 deg. on gauge = 185 deg. F on sensor
1/8 deg. on gauge = 167 deg. F on sensor

What I really need for perfect results is an electronic heater for my oil bath that holds temps real stable.

[DMC5180]

You need one of those portable Inductive "hot plate" cookers "as seen on tv" product. you can set and hold the temp just like an oven.

Unfortunately the units are about $100 at Walmart.


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[Bitsyncmaster]

You need one of those portable Inductive "hot plate" cookers "as seen on tv" product. you can set and hold the temp just like an oven.

Unfortunately the units are about $100 at Walmart.


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I have a real accurate warming plate I use for my epoxy potting but I don't think if goes much above 200 deg. F. It only has a 75 watt heater.

[Bitsyncmaster]

I finished with the hot oil testing (calibration). I wrote the software to give me 29 steps of the gauge reading between the 1/8 position to the 260 deg. position. I would not need all of that range but it lets users run the unit with a sensor that is not really calibrated for our gauge.

I've got my electronic otterstat now controlling the fan (OEM otterstat disconnected) but what I'm thinking of doing is install one of the higher temp otterstats and that will be my backup. Not that I expect any failures but my unit depends on the gauge and sensor remain working. The OEM otterstat does not need any of that gauge circuit to work. I see DAP has three ottersats to choose the switch temp from.

The user can hear the buzzer by setting the lowest setting and warming up the engine until the "over temp" warning comes on.

I will make the few circuit board changes and place an order for 100 boards soon.