Help for Job Interview

Hi Everyone,

I am applying for a water and waste water utility job. In the application it states that you should have experience with "potential differential modulators". I've been around the instrumentation and controls business for 22 years and have never heard of such an animal. I searched Goggle and PLCS.net and got no hits. So I don't look ignorant by guessing during the job interview, I thought maybe one of you might be able to help identify the critter. My guess is that it might be a name that one of the locals use to describe some more common device.

Thanks,

Andy

I've never heard of "potential differential modulators" either, but I've only been in the wastewater business for thirty years. I looked in a couple of my wastewater instrumentation handbooks and couldnt find that critter there either.

I will make a SWAG (Scientific Wild A$$ Guess) that they are talking about some kind of valve postioner that is using voltage as the analog position command. This may even be based on a potentiometer generated signal.

I'd recommend that if it comes up in the interview, just say you don't know that term, and ask what they mean by it. Then you may be able to say, "Oh, I'm familiar with that device, but I know it as XXXXXXXX".

I don't know if it applies to this situation, but remember this: When a headhunting agency is conducting the search, the person who writes up the blurb quite often has no clue what the terms mean.

If you understand most of the technical jargon in the list of qualifications, don't be afraid to admit what you don't know. If you don't understand any of the jargon, you probably shouldn't be applying for the job in the first place.

Tom and Steve,

Thanks for replying. You two are always a great help. I’ve done some work in WWU’s before. I’ve worked on some gnarly equipment and am wondering why I’m even interested. I guess it’s close to home, a road job, they are automating the remote stations, and the pay and benefits are good. It gives me comfort that neither of you have heard that term. I also appreciate the interview advice.

I didn’t list my WAG’s in my question so as not to influence any responses. So here are my WAG’s:

LVDT (Linear Variable Displacement Transducers / Transformer) or RVDT (Rotory Variable Displacement Transducers/ Transformer) or as Tom suggests, a potentiometer based transducer modulating a valve.

Differential pressure transmitters or two pressure transmitters feeding a variable speed drive.

Thanks,

Andy

LVDT

Navy hovercrafts have four rudders (2 per propeller)using hydraulic ram actuators. Each hydraulic ram have an integral control/feedback electronics called LVDT or Linear Variable Differential Transformer

Linear Variable Differential Transformer

Click to expand...

That's what I thought. Apparently they go by another name:

http://www.sensotec.com/lvdt.asp

(It's been years since I've used one, I had forgotten about them entirely).


John

Hovercraft LVDT's control the actuator solenoids based on commands from the pilot/driver. It also measures the actuation and sends a feedback and indication to the AMS monitor.

Hi Andy,

It exactly the same as Tom has said, but i elobrate a bit more.

In our work place it is used to control boiler pressure.

It is a simple wire wound straight resistance with centre as a movable point. centre pointer (set point) rest on a diaphram of pressure line, other two end conected to actuator or to motor through a brige circuit. suply is conected to center point. when pointer in a center, potential on both side is equale but when center point move due to rise of pressure (in my case) pointer moves to one side, now potential is not same. differance of potential is cause to open gas valve to increase the firing rate of boiler. Pressure rises and pointer move back to set point. If presssure decreases vise varsa.

You just described how LVDT on a hovercraft rudder works

Under the right conditions, I think a boiler can BECOME a hovercraft, though I wouldn't want to be in the vicinity if that happened...

beerchug

-Eric