Moore I/P problem 771 series

Hi guys,
Frustrated!!!! ready to beat it up!
I trying to use a Moore I/P P/N 771-16-SN-F2. SD771 model series 771.(Info: 4-20 ma signal input. max 30 Psi. Manual recommends 20 Psi Input pressure.)
I'm applying 20 Psi. using a 4-20ma source from a fluke 707 calabrator. I'm using a fluke 713 pressure calabrator to measure output pressure.

I'm constantly measuring 1.6 psi (most likly leakage pressure)when i change from 4 to 8 to 12 to 16 to 20ma. there is no change in output pressure. I looked at manual, the shipping screw and operating screw seems to be in the correct position. I also tried zero adjust and no out pressure change. I need 6-18psi to get full valve travel.

I tried 3 other I/P's identical to this one and got same results.
I tried a different brand, with the same test equipment, and got my desired results.

am I forgetting something? Any suggestions as to solve this problem. I'm thinking it may be somthing i'm not seeing.

Thanks for the help.

Terry

Terry, from what you describe, things should work just fine. Are you talking about an I/P from Moore Industries? Their website did not yield any info on the model you have. They are at: http://www.miinet.com/ so maybe I have the wrong Moore. But, unless you have three bad I/P's from the same company, I would look further at what is needed by this thing to work properly. Not likely that you have three bad ones from the same company, but it is possible! You could always just use the one from the company that does work and go from there, but then you are probably like most of us in this business, the problem you are having just drives you nuts!

Thanks, and yes your right it is driving me nut's. it don't make any sense. Siemens owns moore now so you may find the manual on their site if not I will copy and post the manual. I was hoping that someone may have used this one before. When I get a chance I will post a photo of the I/P. The other problem is that I may be able to use the other I/P's that I have, but I need 6-18 Psi for full valve travel. I don't know, yet, if I can calabrate the other I/p's for this. When I get a chance I will look up their manual.

but that still don't answer is there something I'm missing. I will get back to you soon.

Thanks again.

This may be the one:

http://www.sea.siemens.com/instrbu/docs/pdf/sd771r4_Oct04.pdf

Scanning it, jumped out are: Must be upright for 15 minutes or damping fluid be wrong, input polarity, etc.

From what I can tell you are using the standard model. This thing will only allow 0.16 SCFM of flow. If you have any type of leak downstream of the I/P output you will probably flow limit through the I/P pretty quickly.


Just a thought
Keith

red98 that's the one. The polarity is correct. I did the exact same thing with another I/p (Powers Process Control)P/n 512-510.
Worked like a charm. I have a bad feeling that the zero adjustment may have been damaged on the moore I/P's. Do you think this could cause the symptoms I described? They are used in a lab enviroment where Instrument students learn to calabrate. You wouldn't think that they would have damaged four of them. but you never know....
Other then that I can't think on anything else to check.

kamenges, I don't understand???
Can you explain what you mean?

This I/P transducer operates by metering supply air out of a small oriface into the output chamber. There is another larger oriface into the output chamber that bleeds to atmosphere. The voice coil in the I/P presses a plate against the exhausting oriface to control the amount of air bleeding from the output chamber. As an example assume the output pressure is currently zero and the command pressure is 10 PSI. The voice coil will seal the bleed oriface until the output chamber pressure exceeds 10 PSI. At that point the pressure in the output chamber overcomes the voice coil force and pushes the plate off of the regulating oriface. This will cause air to bleed out of the output chamber, the output chamber pressure falls a bit the plate moves closer to the regulating oriface and the output chamber pressure increases. In reality an equalibrium results with the plate floating a very small distance from the regulating oriface breeding just enough air so the output chamber pressure can't increase.

This all hinges on the supply air metering oriface. The flow rate of your I/P output cannot be greater than the flow rate through the metering oriface. The metering oriface is pretty small. If your flow requirement is greater than the flow capacity of the metering oriface you won't be able to build any output chamber pressure.

My point was to make sure that whatever you have connected to the output of the I/P needs to be very well sealed. 0.16 SCFM isn't much airflow. It is the quantity of air at atmospheric pressure that is inside of a 150mm^3 box. So a fairly small leak could cause you trouble.

Keith

sirhiss2 said:

I have a bad feeling that the zero adjustment may have been damaged on the moore I/P's. Do you think this could cause the symptoms I described?

Click to expand...

Maybe. Some I/P's are rugged, others fail if the supply air is +5psi above spec.

They are used in a lab enviroment where Instrument students learn to calabrate. You wouldn't think that they would have damaged four of them. but you never know....

Click to expand...

Ahhh, we all have seen situations that when one item doesn't work, we substitute another, thinking that it's bad, but by the time we get to the 3rd or 4th one, realize that maybe we're making them bad by how it's being hooked up / used. Perhaps that what the students did. They let the smoke (or silicon fluid) out.

Other then that I can't think on anything else to check.

Click to expand...

I'd follow the manual for teardown, maintaince & calibration. All the basic checks. And then send them back for repair.

Thanks guys,

Red 98, Thats what I will do.
Thanks for the explanation kamenges.

I wouldn't always blame it on students.

It could have been anyone who was not familure with I/P's although they thought they were, if you get my drift.

My moto is "Read the Manual first!" it helps to avoid such problems as this.

Thanks again.