Gauge calibration help

[MGKelly]

Hello.

I need some help calibrating my temperature gauge. as you can see in the picture at 73 oHMs I'm set to 120 degrees. when set to 10 oHMs I'm at the maximum 250 degrees.
the problem is when i set to 23 ohms the needle doesn't settle in the middle and can't calibrate it without moving from the min and max temperature setting.

Any help or suggestion? thanks, Joe

 

[RJRENTON]

Hello.

I need some help calibrating my temperature gauge. as you can see in the picture at 73 oHMs I'm set to 120 degrees. when set to 10 oHMs I'm at the maximum 250 degrees.
the problem is when i set to 23 ohms the needle doesn't settle in the middle and can't calibrate it without moving from the min and max temperature setting.

Any help or suggestion? thanks, Joe
View attachment 911303

I believe the function of the instrument is it literally a volt meter driven the 5 volt constant voltage source (instrument panel voltage regulator) and a variable voltage divider, aka sensor, or in this case, the temperature sensor is negative coefficient resistor, exhibiting low resistance when temp goes high. Is it possible that your temperature sensor is faulty? The other two instruments, oil pressure and fuel level function similarly. Are you getting a constant 5 voltage to the instrument? The origional IP voltage regulator is also a thermal device, literally a percentage cycle timer, calibrated at approximately 40% on 60% off to yield approximately 5 volts output with 12 volt nominal input. Perhaps you should consider using one of the electronic IP regulator offered by RT Engineering as a plug in device.
My origional RS23V0A****** has the origional instruments AND a mechanical oil pressure gauge and temperature gauge using the vapor pressure principle. The fuel gauge is still the origional along with the float device in the tank...whose reading I take with a jaundiced eye... Just my opinion of course.
BOB RENTON

 

[MGKelly]

I'm using a Extech 382275 power supply with a resistor pack. sending a constant 5 volts, with the temperature gauge removed from the cluster with test wires connected directly to the back pins on the gauge. This the original gauge from my 70 RR just replaced the decal.
Maybe i should see if i get similar results with the fuel gauge? I have a feeling the test wire are adding resistance, maybe some thinner gauge wire?

thanks, Joe

I believe the function of the instrument is it literally a volt meter driven the 5 volt constant voltage source (instrument panel voltage regulator) and a variable voltage divider, aka sensor, or in this case, the temperature sensor is negative coefficient resistor, exhibiting low resistance when temp goes high. Is it possible that your temperature sensor is faulty? The other two instruments, oil pressure and fuel level function similarly. Are you getting a constant 5 voltage to the instrument? The origional IP voltage regulator is also a thermal device, literally a percentage cycle timer, calibrated at approximately 40% on 60% off to yield approximately 5 volts output with 12 volt nominal input. Perhaps you should consider using one of the electronic IP regulator offered by RT Engineering as a plug in device.
My origional RS23V0A****** has the origional instruments AND a mechanical oil pressure gauge and temperature gauge using the vapor pressure principle. The fuel gauge is still the origional along with the float device in the tank...whose reading I take with a jaundiced eye... Just my opinion of course.
BOB RENTON

 

[RJRENTON]

I'm using a Extech 382275 power supply with a resistor pack. sending a constant 5 volts, with the temperature gauge removed from the cluster with test wires connected directly to the back pins on the gauge. This the original gauge from my 70 RR just replaced the decal.
Maybe i should see if i get similar results with the fuel gauge? I have a feeling the test wire are adding resistance, maybe some thinner gauge wire?

thanks, Joe

It can't hurt to check the fuel gauge as well. The test wire's resistance MAY influence the instrument's operation slightly but not to the extent exhibited. Is it possible that the thermal element of the instrument has changed value or was damaged in some way or the pivoting action of the pointer mechanism binding? Just a thought.....
BOB RENTON

 

[MGKelly]

it's possible, but it moves smoothly from one side to the other, doesn't look like there's any interference.

It can't hurt to check the fuel gauge as well. The test wire's resistance MAY influence the instrument's operation slightly but not to the extent exhibited. Is it possible that the thermal element of the instrument has changed value or was damaged in some way or the pivoting action of the pointer mechanism binding? Just a thought.....
BOB RENTON

 

[MGKelly]

fuel gauge is spot on with the same test.

 

[RJRENTON]

fuel gauge is spot on with the same test.

Well, it sort of points to the temperature sensor or a bad ground (?) or connection to the instrument printed circuit board or possibly the bulk head connections..... again, just a thought...
BOB RENTON

 

[Nacho-RT74]

Have you played with both adjusters?

And maybe a stupid question.
Have you checked the needle is correctly seated the internal hooks?

 

[MGKelly]

Yes the needle is seated correctly on both hooks. I tried tweaking the adjusters several times.
I tweaked the unit to fine tune the minimum and maximum temp values, just think there’s something I’m missing. I really don't think the unit is bad.

Have you played with both adjusters?

And maybe a stupid question.
Have you checked the needle is correctly seated the internal hooks?

 

[MGKelly]

Quick question, if the low end and the top end for example 10 oHm and 73 oHm are calibrated correctly does the mid calibration have to be spot on also?
Does it really matter because the mid zone seems to be in the accepted operating temperature?
thanks, Joe

 

[SureGrip]

Quick question, if the low end and the top end for example 10 oHm and 73 oHm are calibrated correctly doe the mid calibration have to be stop on also?
Does it really matter because the that mid zone seems to be the accepted operation temperature?
thanks, Joe

I calibrate sensors for a living.

If you're good at the high and low end, you ought to be just fine in-between.

 

[Cranky]

Is there any way you could check this gauge on a running vehicle? One of the things I've always done is to check the factory gauge with a mechanical gauge or even a lab type thermometer sticking in the radiator neck. And yes, you can get an engine up to operating temp with the cap off the radiator.....just so long as you have tank capacity to 'see' the coolant and not overflow.

 

[MGKelly]

I couldn't try that test right now. Probably buy another temperature gauge, calibrate it and compare the difference.

Is there any way you could check this gauge on a running vehicle? One of the things I've always done is to check the factory gauge with a mechanical gauge or even a lab type thermometer sticking in the radiator neck. And yes, you can get an engine up to operating temp with the cap off the radiator.....just so long as you have tank capacity to 'see' the coolant and not overflow.

 

[dsd1967]

Could you use your voltage source, the sending unit and a pan of boiling water. Use a cooking thermometer to check in between temperatures.

Just don’t let your wife catch you

 

[Cranky]

Could you use your voltage source, the sending unit and a pan of boiling water. Use a cooking thermometer to check in between temperatures.

Just don’t let your wife catch you

I can do that now and not worry about it!