Posts Tagged pressure transmitter

Tips for ranging a vacuum transmitter

0-30 vacuum pressure gaugeA process plant’s technician was mystified about how to get a typical gauge pressure transmitter to read in the vacuum range. “All our gauges are 0 to 30 inches mercury, and that’s what we need to transmitter output to be. But the transmitter you sent us just stays around 4mA when we pull a vacuum.”

We walked out to the reactor vessel to look at the installation. The transmitter’s Low side port was open, its high side port was plumbed into a tee along with a conventional bourdon tube pressure gauge reading gauge pressure vacuum.

I could see why he was confused. The mechanical gauge goes from 0 to 30. I asked what range he used to configure the pressure transmitter. His answer, “0 to 30 inches mercury, same as the mechanical gauge.”

So, what was happening?

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Honeywell smart transmitter design makes communication card swap easy

It was bound to happen sooner or later.

I took a call from a customer who needed to replace a garden variety differential pressure transmitter… with one exception: He needed Honeywell’s DE digital protocol for communicating to his DCS. The DE protocol is still great, but since so many installations today use HART or Foundation Fieldbus, all of our in-stock pressure transmitters had a HART communication card – a critical mismatch to what the customer needed.

A year ago, we would have been stuck rush-ordering a unit from the factory, with all the attendant delays and expediting charges, because you couldn’t swap out a comms card without making the transmitter’s hazardous approval invalid.

What could we do?
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Wet rhymes with Set (or how to remember LRV/URV configuration prompts)

Lots of people like the pushbuttons on industrial pressure transmitters because the basic settings that every transmitter needs can be set up without a HART communicator. This includes things like the tag name, engineering units, LRV (Lower Range Value, the zero, or what 4.0mA represents), URV (Upper Range Value, the span, or what 20.0mA represents) and damping (an average or filter factor that dampens noise).

Honeywell ST700 ST800 configuration screenOn the new Honeywell ST700/ST800 series smart transmitters, the tag name and engineering units are easy to configure and self explanatory, but I seem to stumble when setting up the LRV and URV because I’m faced with a non-descript choice. There’s two sets of options (under Transmitter Setup, not Calibration):

Enter LRV
Enter URV

OK, either configures an LRV or a URV value, but which is which?  What’s the difference?

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How can I keep the water out of my transmitters in washdown conditions?

Earlier this week, I took a call from a customer having problems with his pressure transmitter.  He’d figured out that his last transmitter, installed in an area with nearly continuous wash-downs, had failed because of water intrusion.  The bigger problem was that it wasn’t coming from a loose cover, a conduit pipe, or a leaky conduit connection.  In his case, the water came into the transmitter through a vent hole and messed up the measurement cell electronics.

So he asked me to recommend a 3000 PSI transmitter that could survive the washdown conditions.

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Using a wireless radio battery to power a pressure transmitter

In an ideal world, every place you need to install a transmitter would have easy access to electrical power. But we don’t live in the ideal world, and there are locations where power isn’t readily available, and getting electrical power to those areas can be quite costly.

This was the situation at a local plant, in their flammable fuel storage facility. The site is required to keep a record of the line pressure that supplies water in the event of a fire.

The Problem

The water pipe is located 6 to 7 feet (2 meters) below grade, and the engineers planned to build a vault where they could install and maintain the necessary submersible pressure transmitter.

The planned location is more than 500 yards from any available power source. The signal coming from the pressure transmitter would have to run that distance plus an additional 200 yards to reach the control room.

Not surprising, the trenching cost for an electrical installation was quoted at a five-figure minimum price.

Finding a solution

The project engineer started considering a wireless solution, and then asked, “Can a battery-powered industrial radio also power a two-wire loop-powered pressure transmitter?”

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How do I set upper range value and lower range value on a Siemens pressure transmitter?

A customer needed to re-range a Siemens SITRANS P DS III transmitter without applying pressure. He’d read my earlier blog post about using the pushbuttons to program the DS III (Pressure Transmitter Pushbuttons to the Rescue!), and where to find the Z-fold instruction sheet.

All was going to plan, until he started looking for the settings for lower range value (LRV) and upper range value (URV). And then, in an all-too-familiar scenario, he hit a roadblock. The instructions don’t actually mention URV and LRV, the terms he’s familiar with, by name or acronym. So what’s a guy to do?

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Pressure transmitter pushbuttons to the rescue!

I took a call the other day from a contractor. He was at the construction site, on deadline, and frantic. He was trying to set the zero and range on a Siemens SITRANS P DS-III pressure transmitter‘s 4-20 mA output. He had a HART handheld communicator, but no device descriptor file (DD) that made the two talk to each other. 

Could I help?  Sure! I just asked, “Do you have a Phillips screwdriver?”

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