Relatively Cheap Pressure Transducers

[salvageV6]

Here's a link to some $125 pressure transducers that should work well with data logging systems, or stand alone diagnostic, gauge, or emergency boost control uses with an alky. kit for the DIY'er of course.

General Industrial Pressure Transducers 0.50%-Industrial Automation

Using a 1% 250 ohm resistor accross the 20ma output would give you 0-5 volts for your typical logger.

8-30 Volts excitation which would work fine with auto. voltages.

0-300 psi. model would work great for larger pumps.

[Steve Wood]

Not a bad deal...bit confused tho.

Looks like the output is rated either 0-5 or 0-10 so how do you know which is which...or am I misreading it?

Sure like to log pressures

[salvageV6]

The output on one type model is 0-10 volts, so if you bought the 0-600 psi. it would give you 5 volts at 300 psi.

I wouldn't buy that one however.

I'd buy the current output model, 0-300psi., and it outputs a current signal of 4 - 20 ma over the full range of pressures.

You take a 250 ohm resistor, as accurate as you can buy, 1% will work fine, .1% accuracy would work even better, and place it accross the output terminals of the device. Temperature stable ones are used for this type of work. Easy to find a Newark Electronics or Moser etc.

As the current passes through the stable resistor you get a fixed output voltage, which would be 5 volts at full output or 300psi.

You simply make a scale from there, 0 psi. should be 4ma. through the 250 ohm resistor or 1 volt. Have to check that under use to be sure however.

Easy to do with the 4-20ma output version.

Some data loggers are set up to read this output from transducers.

It's an industry standard type output.

You may need to stabilize the input voltage to it, but the device may do that internally as well, not sure on that, but getting a fixed 9 volt supply voltage for it from a car battery signal is very easy for about $3 tops.

I think I have a box of 250 ohm good resistors, if you buy one, I can send ya a couple.

[Steve Wood]

Thanks for the info!

Somehow I suspect very few pumps ever see 200 psi, but....

[salvageV6]

They do make a 0-200psi. model which would probably work just fine for 99 44/100% of the peeps out there.

When you hit 200psi. you probably have a clogged nozzle or three.

[Scott-N-GA]

What about relatively cheap flow switch, got a place to buy one of those. I want to hook up one to turn on the power injection light in the dash. Pump is progressive controlled so cannot use the pumps power.

Looked through grainger and a couple other places everthing is large and expensive. Cooling mist had one but it was a little pricey also.

Scott

[salvageV6]

They are a bit trickier to find.

I tried a cheap plastic based one years ago, reed switch type, and it didn't work well for me, had to be plumbed in vertically and was inconsistent.

You could make a window voltage comparitor and use the pressure switch to turn on a light.

You could have it run a relay and output 12 volts to a bulb when the pressure is within a specified range with the pressure transducer.

If it got under or over pressure you could use a comparitor and output an alarm or warning light as well.

Overpressure would be over the maximum you normally use or can use, signalling a plugged nozzle or two.

[Steve Wood]

How much voltage does it take to trigger a relay? Seems to me that the voltage is ramping quickly on the pump and if a relay will trigger at less than 12 volts, it would be easier to turn the light on that way rather than with a flow switch.

Will not tell you if the pump is actually pumping, but.........my audible knock alarm tells me that about the time my foot hits the floor.

[salvageV6]

Radio Shack used to make a nice small 9 volt, low current coil, relay that would probably kick in at 6-8 volts which is early in the pump turn on stage for most progressive controllers.

You could use that to send +12 out of the relays switched contacts to the power injection bulb.

Or use the pressure transducer above and when you hit 10-20psi. of alky. pressure use a voltage comparator circuit comprising of the transducers output and a reference voltage, to drive a transistor that turns on a relay to do the same thing. Easy simple stuff really.

You could use comparators or an LM3914 ladder circuit, to output a row of LED's that would show exact pressure in stages, like a Caspers knock gauge, or provide as much detail as you want pressure wise.

Hook it up to a digital gauge to read direct pressure too.