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Temp and pressure sender accuracy?


turbogrill
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Hi,

 

I recently installed a bunch of temp and oil pressure senders in my car.  Normal VDO, sunpro and autometer stuff.

The ohm values seems to be off a bit, is this expected?

 

For instance the oil pressure sender is 260ohm at 0 psi, should be 240 ohm. 

The temp senders are also a few percent off. 

 

I don't think it matters but curious, are you supposed to calibrate them? (Running MS so that is easy to do).

 

 

 

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On 7/20/2017 at 3:23 PM, turbogrill said:

Hi,

 

I recently installed a bunch of temp and oil pressure senders in my car.  Normal VDO, sunpro and autometer stuff.

The ohm values seems to be off a bit, is this expected?

 

For instance the oil pressure sender is 260ohm at 0 psi, should be 240 ohm. 

The temp senders are also a few percent off. 

 

I don't think it matters but curious, are you supposed to calibrate them? (Running MS so that is easy to do).

 

 

 

It depends on how conservative you are with your temps/presssures before you shut it down / consider it a problem, and how fragile your engine is. I tend to use really low numbers before I consider it a problem, and manage it that way (which may absolutely the wrong way for you, but just my $0.02). That way if the gauge is a little off, I am still safe. Also, I try to get cooling and pressures where they are well within the desired ranges, so if they are borderline, it is usually an early indicator of a problem.

 

All that said, I am trying to implement backup sensors that can send data to the pits...

 

 

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Since you are running a Megasquirt I would lock them down to dead nuts on because it is easy to do.

But as you said not all seem that accurate and I would agree with off the shelf stuff as they all have some differences.

 

We run mostly all mechanical gauges and try to give the drivers a range to watch. Got them to at least check every few laps and 

they find a quick problem and radio it in to let us in the pits make the determination to bring it in. We have been able to save a motor or two.

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I would go with mechanical and high temp and low oil pressure BIG RED LIGHTS like off a trailer . If they light up then he can look hard at the gauges .

At WG in a few second we lost the head and cracked the block and 2 pistons on the TDI. I think if we had lights we would of had a chance but if the driver is running hard the gauges is kind of a after thought !!

Bob Mann

www.DRVOLKS.com

bobtec@comcast.net

drvolkslogo.jpgtdtuninglogo.jpg

 

 

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  • Technical Advisory Committee

@DRVOLKS is spot on. "Idiot lights" are your best bet for conveying a problem quickly to the driver. We have used yellow for coolant, red for oil. Each set for a few degrees/PSI shy of the trouble range for our engine. Avoid the white/blue/green spectrum if you do any night racing because that spectrum will change the driver's pupil dilation much more than red/yellow/orange. 

 

As for the sensors - if it's easy to calibrate them in MS, there's no reason in my mind why not to. But if you're doing that, remember to grab at least 2 data points at each end of the range (more if you're concerned about the linearity of their calibration curve).

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Calibrating Temp sensors are super easy, just boil some water and then measure the temp with a good termometer and the resistance. 

The overengineered method is to run the numbers in a curve fitting algorithm, that mathematical function  can be used very nicely in tunersstudio. (need to account for the voltage divider and bias resistor as well). 

 

With oil pressure i would have to get a mechanical oil pressure gauge and sample some points. 

 

I guess abnormal values are of interest, I have no clue if the engine likes X or Y oil pressure or what coolant temp is good and bad. The engine survived running without coolant for plenty of laps and boiling oil, so don't think it's super sensitive. 

 

Need to figure out how to make the megasquirt dash blink like a Christmas tree if it's out of range. 

 

What about a loud as hell siren? If rpm over 1000 and no oil pressure then enable 120db bomb alarm.. 

 

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