Problem with Transducer on Hydraulic Pump

[BAnderson]

We manufacture a small press line, we have made and tested 6 of these lines. We tested them in our facilities many times (100+ for each unit) with out any problems. When we shipped it to the costumers site all they had to do is run 480v AC to the main cabinet. 2 if the 6 presses the transducer stops working after 10 – 30 cycles. If they replace the transducer with a new one it will work for 10 – 30 cycles before they have to replace it again. We have gone through 4 transducers on one pump before giving up. We were not able to test all the hydraulic pumps at our facilities.

I have had two electricians from an out side company and 4 controls guys from my company check it out with out seeing any thing electrically wrong. The customer supplied the pumps and the people they got the pumps from will not look at the pump because they are saying it is no way it is them. I had the company that made the transducer come out and they are not sure what it could be. They say electrically there is no way we could fry it (based on the set-up). They suggested some things we could do to lessen the peek surges that hit the transducer, but said the transducer should not have a problem with this.

We currently use a 3000 lbs transducer but also tried a 9000.

Does any one else have any ideas on what I can check or try?

 

[itsmoked]

How about more info?
Be specific with the system info.

What kind of presses?
Doing what?
What is the expected operational pressure?
What do you mean they quit working?
Read wrong?
Read nothing?
What is the basic hydraulic circuit like?

We will get to the bottom of this but just saying, "a press running a few cycles", is not enough to go on.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[BAnderson]

Sorry, below is a little more detail.

Pump info:
Max pressure: 4000 lbs
Application: Pressing metal nail plates into lumber.

Application info:
We run the press until it hits 2000 lbs of pressure they release pressure. We repeat this process over and over about every 8 minutes. We have the peruse transducer measuring the pressure from the manifold to the press.

Transducer:
Name Brand: Hydac
Max PSI: 3000 measured and 4500 before breaking. Also tried a 9000 psi
Signal: 2 – 40 ma

Electrical:
PLC: Koyo

 

[itsmoked]

Excellent info thanks for the added stuff. Let me cogitate on this for a few minutes.

Which model number xducer?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[BAnderson]

hda4475-a-3000-000

 

[itsmoked]

Okay.. You aren't clear on how the transducers "stop working" so I will offer on both.

You need to make sure that your supply voltage is not exceeding 30V. If voltage spikes are occurring and you are pressing the limits this would take out a thinfilm sensor quickly.

Perhaps solenoids are being run on the same supply voltage,(a bad idea), and they are spiking the supply.


My suspicion is that you are nailing the sensors with a pressure spike. The spike can be vastly faster than any gauge you have. Also you can have you sensor mounted 'just so', so that pressure spikes are maximized for your sensor. Say the end of a long pipe that is 'tuned' such that reflections etc, hammer the sensor. Another is oscillations that are like ringing, that cycles the gauge element rapidly bringing dynamic forces to destructive levels. This can be caused by things like the metal plates suddenly penetrating the wood after a pressure buildup in the normal course of events. Or a valve closing with no shock absorbing accumulator.

Without a doubt the first thing I would do is add protection to the sensor. They are called Pressure Snubbers and are used on gauges and transducers all the time.

Here are examples:

http://www.grainger.com/Grainger/ww...entSearch&originalValue=snubbers&L1=Snubbers,

For a better descriptions go to:

http://www.mcmaster.com/

PAGE 567

These devices buffer any pressure wave fronts coming to the sensor but will not alter your system. Just unscrew the transducer, screw one of these in, and screw the transducer back in. Make sure you get one rated for 4000psi.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[danw2]

I've used Mid-West Instrument's model 200 "Gauge Minder" because it has spring loaded/adjustment for the shutoff pressure, rather than a floating ball the requires some amount of flow to move the ball to the shut-off position.

It's saved many a transmitter or mechanical gauge from overpressure spikes.

http://www.midwestinstrument.com/limiting/limiting_main.asp

 

[jraef]

Another possibility along the lines of what itsmoked suggested:

It's possible that someone ran the transducer wires parallel to a 480V cable or wires feeding the pump and as soon as the pump turns on, it is inducing a voltage onto the sensor leads. But if you measure the voltage when the pump is not running, you will not see anything abnormal.

Been there, done that, got the T-shirt and the hat.

 

[Newmanite]

If there is no damage to the face of the transducer(e.g.ruptured from pressure spike damage)then I doubt that there is an issue with pressure spikes causing the failures.
Are you using a diode to prevent any type of back feed into this circuit?(If not try anyway).Cheap low maintenace easy to fit and if its not a problem at least you have eliminated it from any assumptions later????