Digital hardware, transducer suppliers

[viper6383]

We are looking for an economical solution for pressure, force, temp, etc transducers and DA boxes. We will first be applying a DAS to a DIY flowbench via orfice plate methods and then use an elaborate system for our DIY chassis dyno. Any help would be appreciated.

Also would like to employ a separate pitot tube for velocity checks and would like to know how others have done this. thanks

Brandon

[larrycavan]

[1960flh]

Brandon;

I like your enthusiasm as I to am a make it myself kind of guy, here Below is a link to Honeywell, . But to tell you the truth once you can find something that works in the pressure range +- 70 in H20 with the sensitivity needed the cost of transducers and A to D converters alone is more than the Flow Performance FP1 and with the FP1 you get some great flow data software.

JMO

Rick

[1960flh]

Sorry about the links Newbie still learning to post

[86rocco]

Honeywell pressure sensors are nice but kind of pricey, Freescale (a.k.a. Motorola) sensors in the MPX series are very affordable. Check about 3 pages into Blown928 has made used some of these with his system.

[viper6383]

We have been working with DA stuff for years now in engineering. We can build an 8 channel system for less than the FP1 3 channel setup but we don't stop until we have cut all the excessive overhead out of the costs from advertising something as a "special use"

We are still just tryinh to find that one company that sells transducers and boxes for everything at the right price. I am sure the Honeywell stuff is more than we need probably a little pricey but I will look at the link above for some goods. Thanks for all the input guys.

[viper6383]

I will say the freescale stuff seems to be right on with what we are looking for. Thanks for the link.

Brandon

[rusty105]

Has anyone been able to get something like this working at a DIY level. I ordered some sample sensors from Freescale, and was thinking about getting from DATAQ and seeing what kind of results I would get. If I understand all this correctly the ADC has 10 bit resolution. Would this be enough to work with. I am somewhat new to all this, but I think it should, right?? I don't have my bench built just yet, but was going to mess around with a shop-vac and some PVC to see what happens.

Thanks

[jsa]

[color=#000000][quote="rusty105"][/quote]
Rusty,

10bit means 2^10 or 1024 discrete values.

So a 40" H

[rusty105]

OK, so there are 1024 discrete values to work with. The inputs are +/- 10v on the DATAQ unit, but the sensor outputs are roughly 0 to 5V it would be nice to be able to expand this to fit in the -10V to +10V range to get the best resolution. But it is a start. I'll do a little digging and see what I can find.

Thanks

[Tony]

In practice you will usually find that right down at the limit of resolution there will always be some random fluctuations of the last bit or two. This can be due to electrical noise and/or the analog to digital conversion process itself, as well as small real fluctuations in what is being measured.

The solution is to average multiple readings in software to smooth out these small fluctuations. If this is done properly, statistical averaging can actually result in greater resolution than is theoretically possible from the bit resolution.

For instance, if you take a whole bunch of readings and come up with some numbers like 504, 503, 501, 503, 500, 504, 503, 502...... You could generate a continuous running average of the whole lot and end up with a rock steady displayed number like 502.9

The beauty of electronics is that it is quite often possible to take thousands of readings of a sensor every second, average the results, and obtain both a high resolution and an acceptably fast response. It is trading off speed for extra resolution, but as there is usually plenty of excess speed available to trade. This is usually a very good deal for our type of application.

It is not just a case of connecting up all the hardware. Some sort of software signal processing, and a bit of thought, can usually vastly improve the performance of the system.

Just don't confuse very high resolution with high accuracy. Other factors such as temperature drift, hysteresis effects, and linearity come into it as well.

There is obviously no point in having a digital readout display to 6.0004 inches, if the known accuracy and repeatability is only +/- half an inch.

So those that believe fitting digital readouts will improve bench accuracy, it may, or it may not, depending what you have.

[rusty105]