Sensors with resistance outputs

rharris19 · Post by **rharris19** » Wed Jul 17, 2013 4:33 pm

I didn't even think about the gauge having the reference voltage built in and it basically back feeding the wire with that. Thanks for that and the diagram.

rharris19 · Post by **rharris19** » Mon Jul 22, 2013 2:03 pm

I was able to get the voltage reading from the signal line and it was around .06V full and 1.14V empty. I put that into the computer and connected them up, but for some reason, when I connected the line to the Race Capture, it changed the reading on the aux fuel gauge by about 10%. Any idea of what may be causing this?

Post by **brentp** » Tue Jul 23, 2013 11:48 pm

The input to RaceCapture/Pro is likely "dragging down" the signal from your gauge. An adapter is in order:
https://github.com/autosportlabs/analogBuffer

I will email you.

rharris19 · Post by **rharris19** » Fri Jul 26, 2013 8:47 pm

I haven't received an email from you Brent. I would be more than happy to put in that adapter, if you can point me to where I can get it from and some general directions. Thank you so much.

Post by **brentp** » Fri Jul 26, 2013 8:50 pm

Hi Randy, email sent. Sorry for the delay!

PopKorn78 · Post by **PopKorn78** » Tue Mar 17, 2015 2:31 am

Hi guys, I just finished reading this post and I find that I'm really out of your league, I even need help to use the multimeter to find the voltage

I want to wire a temp sensor. I have a AutoMeter 2" WATER TEMP, 100-250`F SSE, PHANTOM gauge and sender installed in the car.

Where do I check the the voltage and ohms, between wich post of the gauge?

Do I need the pull-up resistor or can I tap from the gauge?

Thanks

Post by **brentp** » Tue Mar 17, 2015 4:12 pm

Hi,

is this sensor already attached to a gauge in the car? If this is the case, you won't need an extra pull-up resistor; the gauge provides it's own internally.

To calibrate the sensor, do this:

Measure the following in multiple steps:

1) voltage and temperature when engine is cold
2) volts and temp when engine is 75 degrees
3) volts and temp when engine is 100 degrees
4) volts and temp when engine is 150 degrees
5) volts and temp when engine is fully warmed up (around 200 degrees)

Report these voltages and temps here and we'll help you do the calibration.

Bonus: if you can, take a pic of you measuring voltage at the gauge!

PopKorn78 · Post by **PopKorn78** » Wed Mar 18, 2015 1:17 am

Thanks brentp for the reply.

Engine cold= 8.30 volts
75 degrees= my gauge will not show that low
100 degrees= 8.04 volts
125 degrees= 7.60 volts
150 degrees= 7.15
165 degrees= 6.66
180 degrees= 6.23
195 degrees= 5.71
near 210 degrees= 5.56

This is with the engine not running on cool down. I took the measurements form the ground and the sender terminal from the gauge.

With the engine running, the reading changes when I rev the engine or when I turn on the lights or the rad fan starts.

I find that the readings are high compared to what people are posting. Did I checked it wrong?

I can only attach 3 pictures, please send me your email by pm and I will send you the rest.
Thanks

Post by **brentp** » Fri Mar 20, 2015 4:17 pm

Thanks for the information. the voltages on your gauges output higher than the 5v input range on RaceCapture/Pro. In this case, we recommend a dedicated sensor. Some gauges output a lower range, and other gauge systems, like the Autometer Elite series have 0-5v datalogging outputs.

We have a list of recommended sensors here:
http://autosportlabs.net/RaceCapturePro ... re_Sensors

We like the AEM 30-2012 sensor because of it's 1/8 NPT fitting - it's compact.

PopKorn78 · Post by **PopKorn78** » Fri Mar 20, 2015 5:59 pm

If I use the sensor with a pull-up, would it work?

Post by **brentp** » Fri Mar 20, 2015 6:06 pm

Unfortunately, a pull up won't do anything for you.

You can create a voltage divider with two resistors that will drop the sensor output to something RCP can handle.

example:

you'd use a 6.8K and 4.7K resistor in the configuration in the image.

Once you have this figured out, you can re-do your voltage measurements at varying temperatures as you did in the first step.

-Brent

PopKorn78 · Post by **PopKorn78** » Sun Mar 22, 2015 7:32 pm

I did like you said and the voltage is good now. 3.77v at 0 and 2.31 at 210, but I don't get the same reading when the engine is running on the dashboard. When not running, I get 190 degrees and when I start the engine, I get 175 degrees. Same for the fuel level. Is this how it should react or I did something wrong?

Post by **brentp** » Sun Mar 22, 2015 7:44 pm

when you say 'dashboard' do you mean the physical gauges on your dash?

In other words, by introducing the resistors it caused an error in your physical gauge reading?

If this is the case, then you might want to up the resistor values in the voltage divider. try 10x the value - e.g. 68K and 48K. Upping the resistor values will minimize the impact on the gauge reading.

This is one reason why we recommend independent sensors for data acquisition (any why ECUs often have separate sensors vs. gauge sensors). You can get it to work, but will require extra effort.

PopKorn78 · Post by **PopKorn78** » Sun Mar 22, 2015 9:01 pm

No, not the physical gauge. I mean the one in the dashboard of RCP app

Post by **brentp** » Sun Mar 22, 2015 9:40 pm

Understood. can you share how you have the analog calibration set up?