Pressure transponders unreliable?

[disquek]

This is not about RT sensors in particular.

I'm trying to build a new DAQ install. This install has pressure transponders for front brake, rear brake, fuel pressure, and oil pressure. As I posted here, the brake pressure transponders read 95 psi high. RT has a work around, but the senders are still not to spec.

The oil pressure transponder (bought elsewhere) has been fine (I think). I reads 0psi at 0psi and when I turn over the motor on the starter it read about what it should 50 ish.

The fuel pressure transponder (also bought elsewhere) read high out of the box (8psi at 0psi) and varied wildly with vibration. I double checked everything, still bad. Bench tested, stil bad. I sent it back and got a replacement. Same thing. Double checked. Bench tested. Still dead.

So I went to a different manufacturer, and was careful to test it on the bench. It worked fine. I installed it (triple checked all connections - heck it's three wires, its not that hard), and it was dead as a door nail. Rechecked everything again, still dead.

So that's 5 sensors dead or off .... out of 6.

Are these things usually this unreliable? I've heard that they're intolerant of vibration. They're all mounted to the firewall and the motor has never even been started.

Thoughts?

PS: yes the grounds are good.

-Kyle

[tristancliffe]

I've had, over the years, a few pressure sensors. Some became ill (VariOhm had a problem with a particular design that would let the medium leak out), but all remained working.

Never tested them to see if the calibration was correct, but never had any odd looking traces, or non zeros where there should be zeros.

Sounds to me like your either using the wrong calibration, or inserting it wrong (brackets are important).

[disquek]

Thanks for the input.

Calibrations are irrelevant here, although they show wrong on the DAQ, I bench test them with a VOM and they show the wrong voltage output.

Mounting them (in the case of the fuel pressure sender) is simply screwing it into the fuel block (1/8 npt) which lives on the frame (not the motor - which has not even been fired yet).

Let's focus on the senders and not my install. I'm 100% sure my install is correct in each case. I've wired FAR more complex things than this without issue. I've triple checked the install and bench tested and double checked the bench tests. These are failed transponders, not an install issue.

I want to know if others have seen transponders fail often.

[blentz2]

Kyle,

I don't run any pressure sensors on the DL1, but the pressure sensors for the CDS system in the GT2 car have been flawless for like 8 years now. You could call Peter at CDS and see what he has for you. They are pretty pricey though.

Also - looks like we're going to have a hell of a race at VIR - get that car done!

[disquek]

Thanks Bobby. Hoping to see you there. The gating factor looks to be my health and not the car's heath. I'll be there either way. If my neck is still down, I'll come with Chris Howard as crew.

I never figured out the issue with the first vendor's sensors, but the second set was diagnosed as follows:

It turns out that this is the result of a flaw in the design of the autometer senders and connectors. The senders have their atmospheric reference port inside the weather proof connector (metri pack). When you attach the connector, it compresses a small amount of air in the connector. The connector seals so well that this compressed air does not leak out.

This means that the reference port side of the sender is seeing pressurized air, and this results in an artificially low (negative at 0) pressure reading.

Venting the connector (drilling a small hole in it) solves the problem.

Users of the autometer gauge would never see the problem, since the gauge would simply read 0 at 0 (although the sender would be sending a negative value - the gauge has no ability to indicate less than 0). They would then get inaccurate (low) pressure readings from the gauge. A classic case of manufacturing screwing up design.

This was not as easy diagnosis!

Still no idea why the RT brake pressure senders read high (80-95 psi at 0).

-Kyle

[blentz2]

So, you got autometer senders to work?? They are pretty cheap and would be worth trying - can you enlighten us as to how to do this? temp sensors too?

thx!

[WillM]

This is a little tangent from the topic, but Autometer Elite series gauges provide 0-5v sensor output signals, and work extremely well with my DL-1.

The gauges are expensive, but are quality made and offer LED illumination and programmable warnings lights. The entire gauge face acts as the warning light and can be programmed to changes colors and flashing status at user-defined set points. For example:

Danger Low: Flashing Blue
Warning Low: Solid Blue
Normal : Solid Green
Warning High: Solid Red
Danger High: Flashing Red

It is also very nice to have one sensor serve three purposes: a gauge, warning light, and data system.

I have a water temp, oil pressure, and oil temp gauge. Setups is easy, as Autometer includes sensor variables in the instructions.

[disquek]

WillM,

As an experiment try removing the seal from the pigtail of your pressure sender and see if you get the same result. The seals come off and back on very easily.

It maybe a very slight difference if you have 100psi senders (oil pressure) since the seals likely only create a few psi of pressure when inserted. If you're measuring fuel pressure in my case and you're looking for only 4psi (Weber DCOEs), it's a very large discrepancy.

-Kyle

[WillM]

Hi Kyle,

I will try that next time I have a chance. Probably early next week.

I'm very interested to know how these sensor issues pan out for you. I'd like to implement a few more pressure sensors (brake) into my DL-1, but am weary of these issues and having to deal with them. The sensors aren't cheap either...yikes!

[WillM]

Kyle,

Are these Bosch/BMW pressure sensors the same as the sensors you purchased?

Pressure-Sensor-for-DSC--ABS-Pump-E39-01-03-525i__34511165467-BOSCH-E39525

According to the link above, the BMW part number is: 34-51-1-165-467

A Google search of the BMW part number returns this discussion:
http://forums.corral.net/forums/showthr ... ?p=9599071

Which links to this:
http://apps.bosch.com.au/motorsport/dow ... essure.pdf

The technical data of which (sensor 0 265 005 303), matches RT's sensors identically.

[WillM]

WillM,

As an experiment try removing the seal from the pigtail of your pressure sender and see if you get the same result. The seals come off and back on very easily.

It maybe a very slight difference if you have 100psi senders (oil pressure) since the seals likely only create a few psi of pressure when inserted. If you're measuring fuel pressure in my case and you're looking for only 4psi (Weber DCOEs), it's a very large discrepancy.

-Kyle

Hi Kyle,

I was finally able to get this done. I did not perceive any difference before/during/after removing the seal. My system does indeed go to 100psi. It is certainly possible that a 0-15psi sensor would have shown a difference, but my 0-100psi did not.

Cheers,

Will

[osborni]

The senders should be remote mounted to avoid engine vibration.

High heat will also make them flake out. Most common industrial ones have a ~100*C temp limit. So mounting them directly to an engine mounted oil manifold or coolant radiator is a bad idea.

I have all my pressure senders on an4 lines and move out of heat and vibration locations. No issues at all. Using honeywell and msi stuff. They are still in the engine bay.