Technical > Wiring & Sensors

Calibrating temp sensors

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se7ensport:
Now it's up and running I need to recalibrate the two temp sensors, on megatune they are showing circa 25 degrees when the actual temp is closer to 15, how do I do this?


Cheers

Alex

dnb:
First of all, you need to know the resistance of your temperature sensor at a couple of known temperatures.

You can then either construct a curve of this and make up a calibration curve file (I have a spreadsheet to do this) and patch it into the VEMS firmware using the hexpatch utility, or use one of the calibration curves supplied with hex patch, based on knowing that you need to change the readings by 10 degrees at 15C -   chances are there is a curve that is OK for your sensors in the hex patch directory, so there's no need to do things "the hard way" yourself.         
Both sensors are done in the same way.

I can provide more detail tonight when I'm not stuck at work.

rob@vems.co.uk:
Are you  using the Bosch sensors from the WebShop?

If so then its a case of uploading the tables using tempsensor_upload.bat (tempsensor_upload12x12.bat or tempsensor_upload16x14.bat for versions above 1.0.72).

You will either need to edit the batch file or use the command line to do the upload.
Close MegaTune.
Use download-config.bat to save your config.txt and tables.txt, these are put in the config folder.
Then using the command line, in the VEMS root directory type: tempsensor_upload 2252 2252 256 and hit return.
This will patch the temperature sensor tables onto the firmware and upload the new image.

After this has run, check your Temps with MegaTune.

If you're not using the sensors then we'll have to work through measuring the resistance of the sensor as various temperatures.

You may find that trying some of the other values may work, if you look in Tools\ntc_airX_cltfactor you'll see files in the format:
airXfactor_2252_256.hex  this is an air sensor that reads 2252Ohms at 25degrees, the final 256 value is the Analog reference value which you needn't worry about as you're only interested in 256 with the units bought from the webshop.

Effectively you have a range of air and coolant sensors: 2252 2400 2700 3000 3300 4300 5600

So if you wanted to try a 2700 air and 4300 coolant you'd got to VEMS root directory type: tempsensor_upload 2700 4300 256 (or tempsensor_upload12x12 if you're running firmware v1.0.73 and above)

se7ensport:
Rob

Both sensors came from the webshop via you, I think the engine temp is bosch (long sender type), and the air is just a resistor that I've made a mount for.


Dnb

There must already be a curve within the data as they both work, just returning the wrong figures by approx 10 degrees.



Both

I follow Robs instructions for downloading and reloading temp file, but how do I know what to adjust within the file or is it obvious? or, as these are standard sensors shouldn't a table already exist with the correct figures that I can just upload?



Thanks for the quick responses, I can't play with it until tomorrow as I'm also stuck at work.


Alex

rob@vems.co.uk:
These are both 2252 sensors (they give a resistance of 2252ohms at 25degC)

Interesting that they are both 10degrees out.  If you can pop the coolant sensor in boiling water and see what MegaTune reads, it would be useful as there may be an offset value wrong in MegaTune - meaning that the temperature calculations made by VEMS are correct, just that they're displayed incorrectly.

Rob

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