Seek Temp vs. Resistance Graph for VDO Temp Sender
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Ron:
The Volvo green book provides one data point - 200 ohms at room temperature (I am going to guess 20C). Not exactly a curve. I removed my temp sensor long ago when I changed my dash. All my D jet parts and a lot of other stuff were sold to a friend who is restoring his p1800E so that he would have some spares. The sensor might have been part of that. If not, it is in my Volvo parts box in the garage. If you can't find a curve I will see if I still have the sensor in the parts box. If I do it would take about 5 minutes to grab 3 measurements and then you could use one of those curve fits to generate an equation describing the curve of the sensor.
On a separate note, I have to admit that I am not feeling the love for this new Swedespeed interface.
The Volvo green book provides one data point - 200 ohms at room temperature (I am going to guess 20C). Not exactly a curve. I removed my temp sensor long ago when I changed my dash. All my D jet parts and a lot of other stuff were sold to a friend who is restoring his p1800E so that he would have some spares. The sensor might have been part of that. If not, it is in my Volvo parts box in the garage. If you can't find a curve I will see if I still have the sensor in the parts box. If I do it would take about 5 minutes to grab 3 measurements and then you could use one of those curve fits to generate an equation describing the curve of the sensor.
On a separate note, I have to admit that I am not feeling the love for this new Swedespeed interface.
142G;
I see the graphs for the FI sensors, but I don't even see the 200Ohm spec for the Temp Gauge Sensor!...where did you see that?
...and I have to agree about the new format...it will take some getting used to...it seems to have less oversight to me...
Cheers
I see the graphs for the FI sensors, but I don't even see the 200Ohm spec for the Temp Gauge Sensor!...where did you see that?
...and I have to agree about the new format...it will take some getting used to...it seems to have less oversight to me...
Cheers
The 200 ohm spec was in the section covering the testing of the gauge142G;
I see the graphs for the FI sensors, but I don't even see the 200Ohm spec for the Temp Gauge Sensor!...where did you see that?
...and I have to agree about the new format...it will take some getting used to...it seems to have less oversight to me...
Cheers
Ron:
The 200 ohm value for the sensor was on page 3-56 of the electrical section of the 1971 140 manual. The section covers the testing and repair of the instruments.
It was a pleasant day today so I went out to the garage to scrounge through my boxes of 140 parts. I eventually found the sensor (of course just about the last zip loc bag in the last box). I was too lazy to set up an ice bath and boiling water bath so I just used my heat gun and measured the outside temp of the sensor using a thermocouple. The measurements I took were
12.5 C - 405 ohms
25 C - 217 ohms
64 C - 30.6 ohms
If you use these values in a Stenhardt - Hart equation Steinhart–Hart equation - Wikipedia
you get this 1/T = .0024458 + .00014068xR + 0.9716506E-6xR^2
Two problems with the above coefficients in the equation. My measurements were very quick so they are very dirty - the temperature measurements are easily out by a couple of deg because I did not wait a long time for the sensor to stabilize and 2 or 3 deg error can make a big difference when the temperatures are small. The second is that the test values are closely clustered and the equation can become dodgy when you use it outside of the test range (the farther outside the worse the possible error). When I calibrated the sensors for my EFI project I used a nudge under 100C (boiling water at my elevation), 50 C and 0C ice water bath for the test values.
The above equation will be 'in the ball park'. Treat as such. For what it is worth, the VDO sensor had 120 C and 12.7 stamped on its body. It is within the realm of possibility that 12.7 is the resistance at 120 C.
The 200 ohm value for the sensor was on page 3-56 of the electrical section of the 1971 140 manual. The section covers the testing and repair of the instruments.
It was a pleasant day today so I went out to the garage to scrounge through my boxes of 140 parts. I eventually found the sensor (of course just about the last zip loc bag in the last box). I was too lazy to set up an ice bath and boiling water bath so I just used my heat gun and measured the outside temp of the sensor using a thermocouple. The measurements I took were
12.5 C - 405 ohms
25 C - 217 ohms
64 C - 30.6 ohms
If you use these values in a Stenhardt - Hart equation Steinhart–Hart equation - Wikipedia
you get this 1/T = .0024458 + .00014068xR + 0.9716506E-6xR^2
Two problems with the above coefficients in the equation. My measurements were very quick so they are very dirty - the temperature measurements are easily out by a couple of deg because I did not wait a long time for the sensor to stabilize and 2 or 3 deg error can make a big difference when the temperatures are small. The second is that the test values are closely clustered and the equation can become dodgy when you use it outside of the test range (the farther outside the worse the possible error). When I calibrated the sensors for my EFI project I used a nudge under 100C (boiling water at my elevation), 50 C and 0C ice water bath for the test values.
The above equation will be 'in the ball park'. Treat as such. For what it is worth, the VDO sensor had 120 C and 12.7 stamped on its body. It is within the realm of possibility that 12.7 is the resistance at 120 C.
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