Infrared Temp Sensor with Automotive temp gauge

[RWB713]

Hello All,

Sorry for the newbie post... and i only have a basic knowledge of what i'm trying to accomplish in relation to the members of this forum i'm sure, but I'm trying to setup on infrared temp sensor in conjunction with an automotive temperature gauge to measure the temp of the drive belt on my sxs...

I am wanting to use this sensor:
https://www.raytek-direct.com/produ...or-vdc-output-with-1m-cable-0-75-16unf-thread

with this gauge:
https://www.glowshiftdirect.com/elite-10-color-water-temperature-gauge/

Limited data is available for the gauge, but I have it in hand and using a MM i measured the following signal voltage while heating up the included water temp sensor on the functional gauge:

280F - .200v
270F - .219v
260F - .242v
250F - .269v
240F - .300v
230F - .337v
220F - .377v
210F - .420v
200F - .465v
190F - .525v
180F - .590v
170F - .670v
160F - .751v
150F - .835v
140F - .925v
130F - 1.030v
120F - 1.145v
110F - 1.250v
100F - 1.355v

No Sender plugged in - 2.45v

Resitance on the regular sender is as follows:
100°F - 6299 ohms
200°F - 1160 ohms
300°F - 323 ohms

The infrared sensor is programmable and has an adjustable output of 0-5v and the scale is adjustable, but from the manual it seems like the sensor sends a lower voltage at lower temp and a higher voltage at higher temps, which is the opposite of what i metered on the gauge.... but with the oem sensor, It has higher resistance at lower temps, which as i understand it, should produce a lower voltage at lower temps...but that doesn't seem to be the case

I don't have the sensor in hand yet, it should be here next week, but any help is appreciated as to what I'm missing and where i need to go from here. This is relatively new concept for me and i'm probably still trying to grasp the basics, but i don't feel what i'm trying to do should be too incredibly hard. Let me know of any other information you may need and I'll see if i have or know it, again, I appreciate anyone in advance who is willing to take the time to help me!

 

[gophert]

The current system has a 5100 ohm resistor feeding the sender (from the 2.45 v supply)

 

[RWB713]

Yes, but the infrared sensor won’t function off resistance, it sends a voltage signal relative to temperature purely based off a processor, at least that’s how I understand it, I could be wrong, but I think the trick will be to get the signal range matched to the normal sensor.

The sensor has a 12v +\- for power, and then a Ts+ and Ts- that relay the voltage signal, another hangup is how to wire that... am I to wire the 2.45v + from the gauge to the Ts+ on the infrared sensor? And then the Ts- to the other wire to the gauge?

It’s probably also worth noting that the voltages I gave above were metered at the two wires that go in/out of the original sensor

 

[RWB713]

This is what I know so far...

Do I need to meter the wire out of the original sensor using a chassis ground to get a different voltage reading @ temp?

 

[rjenkinsgb]

I think you may be able to get it to work with a transistor and a few resistors.

NPN transistor; emitter to - (0V) via a 100 ohm resistor.
Collector to gauge input, the sensor + terminal.

New sensor also connected to 0V and +12V power.

Output from the to the transistor base via a preset pot, eg. 10k, one end to 0V, other end to sensor o/p, with a 1K resistor between the pot wiper and transistor base.
Another 10K preset across 0V & 12V, wiper to the transistor base via a 10K resistor.

The first pot should adjust the "span", how much effect a temperature change has on the gauge.
The second pot adjusts the offset, eg. what the mid point temperature will be.

The two will be rather interactive and it will take several attempts to get them both in appropriate positions; you mal also need to try different values for the summing resistors to the base, if one or the other pot is at the end of its travel..

More complex solutions would be more controllable, but if it's just a one-off it should be OK once calibrated.
If it works OK but fine adjustment is difficult, you could use multiturn presets. Set them to the same position as the old post using a meter, if you do change them..

For a vehicle, it will probably need a voltage regulator to feed the offset bias pot (and possibly temperature sensor), to avoid drift as the battery voltage changes. a 78L05 should be OK for the pot supply, though that may also need a lower value resistor from the offset pot to transistor base eg. 4k7.