Calibrating temp sensors

[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

[se7ensport]

Re: boiling water, would suspending them in a kettle do the job, otherwise I'm not sure how to do it!

[dnb]

I used a cup of freshly boiled water.

[Agriv8]

I used a kettle to check mine ( wife wandered why I ofered to make her a brew  ).
Tropical fish tank ( fish tried to eat it - nothing new there then  )
and a mug of water out of the hot tap all my reading were spot on so didnt need to calibrate.

all checked with the digital thermometer on my multimeter.

regards

Agriv8

[rob@vems.co.uk]

Instead of boiling water you can do the following.

Download the zip file from here: http://www.vems.co.uk/VEMSConfigs/tempsensor_upload.zip

Unzip it into the directory you copied the VEMS CD contents to (we'll call this the VEMS directory).

Close MegaTune.

Open a command screen change to the VEMS directory, and type:
tempsensor_upload 2252 2252 256

Watch the full stops fill the screen.

Restart megatune once the upload has completed.

Check the temperatures.  I've just done this using the stuff I sent you on a generic VEMS, initially the air temp sensor read 31deg, my thermocouple read 19 deg and the house thermometer read 21deg.

After doing the above the Air temp read 22deg my thermocouple read 19 and the house thermometer read 21deg.

Rob

[se7ensport]

I thought I was IT literate  but "Open a command screen change to the VEMS directory, and type:" has got me stumped, really simple explaination required!

[rob@vems.co.uk]

Windows XP:
Start->Run...
In the Open: textbox type cmd

change directory to the place you have the VEMS stuff saved by typing:
cd c:\<directory> changing the <directory> to the right location.
If you're not sure of the location, right click on the upload-firmware12x12.bat in your explorer window, and select Properties, the location is displayed in the second section.
Mine for example says: C:\Documents and Settings\robbo\Desktop\VemsMT1.0.73rc1

We're so close to having a GUI to do this its not funny...

[se7ensport]

feeling further illiterate.....

followed instructions above, unzipped folder and saved the files to the VEMS directory over the top of older versions, opened comand screen, went to VEMS directory, put in tempsensor_upload 2252 2252 256 hit enter and got

'tempsensor_upload' is not recognised as an internal or external command, operable program or batch file.

[rob@vems.co.uk]

I made a fatal mistake...

tempsensor_upload12x12 2252 2252 256

Rob

[se7ensport]

think I've just made a fatal mistake.

followed instructions as above, had it connected to VEMS, lots of figures scrolled by, message at bottom of screen said something along the lines of hello, then it all stopped, nothing happened for a couple of mins so I exited out of screen, started MT and tried to start engine. MT shows no connection to VEMS and engine doesn't start, didn't check for sparks as its getting a bit late, but lack of comms with MT is the concern.

just reread instructions and fullstops didn't fill the screen, I also had the ecu on, was this a mistake as well??

I did download config bat earlier and I have the last lot of settings from MT saved as well.

help.

[rob@vems.co.uk]

This will be fun

Its not the end of the world, but it aint brilliant either.

Grab this:
http://www.vems.co.uk/VEMSTech/VemsMT1.0.73rc2.zip
And we'll go through the setup, probably best on the phone

We can upload the firmware again, it will take a bit of messing around but no one will loose an eye or anything.

Text me when you're in a position to roll and we'll take it from there.

Rob