how to use transistor to increase resistance

Thread Starter

saeidbb

Joined Jan 21, 2022
25
Graphing that data on one chart will certainly help us see how close the curves are. Just looking at the tabulated data shows us that for both sensors the resistance drops as the temperature rises. That is good for us because it means that there does not need to be an inversion section. All that is required is adjustable gain and offset. Now if the data is ploted we will be able to see if there is anything like a LINEAR change in resistance with temperature. That would be handy and certainly make accuracy a lot easier. THAT is why I asked about plotting the data points. It quickly shows us how much gain and offset will be needed.
I uploaded a file that contain a chart of resistance base on temperaturesensor.png
 

Alec_t

Joined Sep 17, 2013
12,818
After placing this circuit, the indicated temperature also increases with increasing resistance, but with the digital thermometer sensor and the car sensor, the resistance decreases with increasing temperature.
In that case it looks as though the two provisos at the start of post #17 aren't met, so my suggested circuit isn't going to work with your digital meter. A pity. My circuit ws originally designed for adapting analogue gauges to cope with various resistive sensors. I don't see any obvious workaround.
It's possible the digital meter doesn't directly sense current through (or voltage across) the resistor, but instead times the charge/discharge of a capacitor via the resistor. If you had access to an oscilloscope you could check for a voltage waveform across the resistor.
 

MisterBill2

Joined Jan 23, 2018
11,919
OK, now it is clear that the two responses have similar shapes, but different slopes and offsets. The good news is that they are much closer toward the high temperature end, where most I.C. engines operate. This means that a simple compromise with gain and offset adjustments can get the readings close for the segment most of the time. In addition, adding a single diode and adjusting resistor to the feedback loop could work to compensate for the divergence at lower temperatures, it seems.
The amount of compensation will depend on how accurate the readings need to be over how big a range.
It might even be possible to obtain adequate accuracy with simply a resistor in parallel with the digital sensor. You can do that on the computer just by adding a fixed resistance in parallel with the digital sensor. When the curves are similar then it will just be a matter of adjusting the gain number.
I hope that my explanation makes sense to you, I know that there are others much more experienced in computer based analysis who participate here.
 

MrChips

Joined Oct 2, 2009
26,145
Find a 9kΩ NTC thermistor and put it in parallel with the W1209 sensor at the same location. You can try a 10kΩ thermistor which is more readily available. I suspect that the W1209 sensor is most likely a 10kΩ sensor in any case.

Or replace the W1209 sensor with a 4.7kΩ NTC thermistor.

Edit:
What I said may not be correct.
What are you trying to do?
 

Thread Starter

saeidbb

Joined Jan 21, 2022
25
Find a 9kΩ NTC thermistor and put it in parallel with the W1209 sensor at the same location. You can try a 10kΩ thermistor which is more readily available. I suspect that the W1209 sensor is most likely a 10kΩ sensor in any case.

Or replace the W1209 sensor with a 4.7kΩ NTC thermistor.

Edit:
What I said may not be correct.
What are you trying to do?
I can not replace the sensor. First I explained that I have a temperature sensor mounted on the car and I want to read the temperature using this sensor with another digital thermometer. But unfortunately, the thermistors used are different, which I posted in the post#22 about the two thermistors (temperature sensors). I have to connect this thermistor to the digital thermometer in a way that the numbers shown are correct.
 

MrChips

Joined Oct 2, 2009
26,145
Where is the temperature sensor in the car mounted or located?
Can you mount the W1209 sensor in the same location?
What is your intended use of the W1209 temperature readout?
In other words, what are you trying to do?

I assume that the sensor in the car serves a certain engine function. You cannot alter this without affecting engine performance.
 

Thread Starter

saeidbb

Joined Jan 21, 2022
25
Where is the temperature sensor in the car mounted or located?
Can you mount the W1209 sensor in the same location?
What is your intended use of the W1209 temperature readout?
In other words, what are you trying to do?

I assume that the sensor in the car serves a certain engine function. You cannot alter this without affecting engine performance.
No, I can not replace the sensor. In fact, the car sensor is a thermo switch of the car itself. In post 21, I have put the part number and its link

In post 26, I explained what I wanted to do. I want to read the car's engine temperature using a digital thermometer. The reason for this is a wrong design of the car company that in my used car, the temperature gauge is fixed in the temperature range of 75 to 105 and does not move. My goal is to have temperature changes in this temperature range
 

MrChips

Joined Oct 2, 2009
26,145
I still do not understand what you are attempting to do.
If you want to readout the temperature of your car engine then mount the W1209 sensor on the engine.
I am not asking you to replace the engine's sensor because we know that that will defeat the purpose of the sensor.

If you know that the car's sensor is working and that it has no engine function except to feed the dashboard gauge then we can find a solution for that.
 

MisterBill2

Joined Jan 23, 2018
11,919
Depending on the range that you need accuracy of the digital display temperature reading, and how close it needs to be over the range of 80C to 100 C, adding a series resistor to the existing digital doisplay connection will get you quite close. For the 70 to 100 degree range the curves of resistance versus temperature are close to parallel. with an added series resistance they could cross at some point, being exactly correct.
Adding a temperature-dependent curve compensation multiplier will be a lot more complex.
 

MrChips

Joined Oct 2, 2009
26,145
If the engine sensor does no other function but to drive a dashboard meter, then put a 4.7kΩ NTC thermistor in series with the engine sensor and mounted in a location similar to the engine sensor. The two sensors now take the place of the W1209 sensor.
 

MisterBill2

Joined Jan 23, 2018
11,919
No, I can not replace the sensor. In fact, the car sensor is a thermo switch of the car itself. In post 21, I have put the part number and its link

In post 26, I explained what I wanted to do. I want to read the car's engine temperature using a digital thermometer. The reason for this is a wrong design of the car company that in my used car, the temperature gauge is fixed in the temperature range of 75 to 105 and does not move. My goal is to have temperature changes in this temperature range
I have seen that arrangement, but not recently. CUSTOMERS WANTED A TEMPERATURE GAGE, NOT AN IDIOT LIGHT. So now we have a curve for some sensor that fits in the same place, I guess.
My first advice would have been to see how close the gage is when you have the correct analog sensor instead of a switch. It might be that the gage is OK with the thermistor sensor that you have. Or possibly not OK, no telling.
When any product is "optimized" for the lowest possible cost to produce, quality is seldom present.
 

Thread Starter

saeidbb

Joined Jan 21, 2022
25
I still do not understand what you are attempting to do.
If you want to readout the temperature of your car engine then mount the W1209 sensor on the engine.
I am not asking you to replace the engine's sensor because we know that that will defeat the purpose of the sensor.

If you know that the car's sensor is working and that it has no engine function except to feed the dashboard gauge then we can find a solution for that.
I know how the car temperature sensor works. Especially in the case of my own car, I thoroughly checked and I can not solve the problem through the car's own sensor
In fact, in my car, the temperature sensor sends the values to the ECU, and the ECU sends the temperature values to an IC in the dashboard, and that IC does the temperature display with a gauge in the dashboard.
Also, because the coolant temperature must be measured, I can not install my W1209 sensor on the car, and if it is installed on the car body, the temperature will not be displayed correctly and it will reach the real temperature with a very long delay.
 

Thread Starter

saeidbb

Joined Jan 21, 2022
25
Depending on the range that you need accuracy of the digital display temperature reading, and how close it needs to be over the range of 80C to 100 C, adding a series resistor to the existing digital doisplay connection will get you quite close. For the 70 to 100 degree range the curves of resistance versus temperature are close to parallel. with an added series resistance they could cross at some point, being exactly correct.
Adding a temperature-dependent curve compensation multiplier will be a lot more complex.
At first I tried to do the same thing, but due to the fact that at high temperatures the change in resistance of the sensor on the car is low and at the same temperature changes in temperature W1209 sensor is relatively higher, the temperature is not shown correctly and even for example with a change of 4 degrees Celsius on temperature The temperature of the car coolant shown by W1209 is one degree Celsius, which is not very interesting
 

Thread Starter

saeidbb

Joined Jan 21, 2022
25
If the engine sensor does no other function but to drive a dashboard meter, then put a 4.7kΩ NTC thermistor in series with the engine sensor and mounted in a location similar to the engine sensor. The two sensors now take the place of the W1209 sensor.
Due to the fact that the coolant temperature is desired, I can not put the new NTC thermistor inside the coolant and I have to put it inside the chamber around the engine, in which case the resistance of the new NTC thermistor added will be different with the ambient temperature changes. Not shown. For example, on a winter day, due to the cold environment, the engine coolant temperature is less, and in summer, vice versa.
 

Thread Starter

saeidbb

Joined Jan 21, 2022
25
I have seen that arrangement, but not recently. CUSTOMERS WANTED A TEMPERATURE GAGE, NOT AN IDIOT LIGHT. So now we have a curve for some sensor that fits in the same place, I guess.
My first advice would have been to see how close the gage is when you have the correct analog sensor instead of a switch. It might be that the gage is OK with the thermistor sensor that you have. Or possibly not OK, no telling.
When any product is "optimized" for the lowest possible cost to produce, quality is seldom present.
In fact, when I check the temperature with OBD2 Diag devices, the temperature received by the ECU is quite accurate and correct, and although the dashboard temperature gauge is constant in the temperature range of 75 to 105 degrees, but the ECU temperature Shows that it is completely correct and when the temperature rises to 96 degrees, the radiator fans start working and turn off at 89 degrees, which is fully visible by the ECU.
 

Alec_t

Joined Sep 17, 2013
12,818
I see your car's sensor is a 4-pin one. Do you have a wiring diagram for it, or know the functions of all 4 pins?
 

Thread Starter

saeidbb

Joined Jan 21, 2022
25
I see your car's sensor is a 4-pin one. Do you have a wiring diagram for it, or know the functions of all 4 pins?
Yes, I know all the pins and I give them their function and I have shown it in the image below.
In fact, the car's temperature sensor consists of two thermistors, one connected to the ECU and one to the car air conditioner, and data is sent to the dashboard gauge from the ECU. Due to the fact that my car does not have air conditioning, these two pins are useless and I used two pins for Air conditioner.Gen2 Temperatur sensor.jpg.
 

MrChips

Joined Oct 2, 2009
26,145
Let me see if I get this right. Correct me if I am wrong.

1) The temperature sensor in the car is working.
2) The dashboard temperature display is not working.
3) You bought this digital thermometer

digital thermometer.jpg
and this thermostat controller, hoping to replace the dashboard display.
W1209 thermostat.jpg

4) The engine temperature sensor is used by the ECU for engine functions.

Here is my analysis.
You cannot replace or modify the engine sensor. The only possible solution I can offer is to tap off the signal from the sensor with a high input impedance amplifier. Feed this information to a microcontroller and convert the data for a suitable temperature display.
 

MisterBill2

Joined Jan 23, 2018
11,919
Actually there is another fairly simple alternative that is not an electrical fix. That is to ADD the digital display's sensor to the car's cooling system. From the photograph, it looks like a 1/4 onch diameter cylinder, welded closed on one end. If that is the case, the a standard fitting to couple 1/4 inch tube to pipe threads is all that you need. You will needto loacte a point in nthe coolant system where you can drill and tap a hole to thread that fitting in. Worst case, you might even need to purchase a pipe-size tap, probably for 1/4 inch NPT threads. Then your sensor can be properly installed to sense the coolant temperature, which I am presuming is what you want to measure. OR if you do not choose to do that, depending on the vehicle arrangement, you could install what is called a :flushing adapter in a coolant hose. OR, possibly there is an unused connection port on the radiator that has a plug in it that can be replaced by your sensor. Certainly being able to use the exact sensor will be worth a bit of research in that direction.
 
Top