Control.com - Nerds in Control

Hello,

Which are your favorites of any type of field instruments, especially transmitters, and why? (Please don't mention the vendors, just the type.) I post this for fun only so don't take it too seriously.

It seems folks are reluctant to respond so I will start with a couple I hate.

Doppler Ultrasonic Flowmeters - I have tried several different brands, now no-one can convince me they even work (Transit time are OK).

Mechanical flow switches (very unreliable).

Roy

The paddle type flow switches work pretty well in clean, non-visocus fluids. If misapplied nothing works very well.

Bob,
I worked in the mining industry for many years. It is common practice for the grinding mill manufacturers to use a very expensive paddle flow switch in the trunion bearing lube oil circuit (very clean oil). A typical mill lube system runs non stop for months on end however I have observed on a power failure less than half of the switches work. Loss of lube oil in this application would be disasterous. For this reason I would never use one in a critical application.

Roy

The doppler flow meter has a VERY restricted application set, but the vendors tend to oversell them into applications where they have high probabilities of failure. They do work -- if you use them correctly.

Walt
Sent from my BlackBerry® wireless device

Walt,
We have all seen the fancy pictures of a sound wave going through the pipe wall and bouncing off a solid particle back to the transducer, I don't believe that. I have tried different dopplers on slurry service and for a while they seem to work but as soon as you turn your back they fail.

You are welcome to that technology.

Regards
Roy

Hello,

I don't know about you guys but it seems that ultrasonic flow measurement still can't overwhelme or even match the coriolis or vortex in slurry materials measurement. According my own experience and observations (or my eyes are tricked) the claims for ultrasonics as "easy mounted, and reliable" hear like rumours and cannot prove well. Any comments?

I work in the alumina industry and I am aware of many trials of ultrasonic flow meters over a 20+ year period without success.

There are some specific theoretical issues with Bayer liquors such as the higher sound velocity and increased acoustic impedance. Even in water it is difficult to analyse all the potential acoustic paths and different transit times. Doppler doesn't simplify anything from a theoretical viewpoint. It might be simple if you have a solid body coming towards the transducer but a bunch of particles at different distances? That's not so easy.

Is anyone aware of any successful applications in Bayer liquors or Bayer slurries?

Vince

In my experience the best flowmeter for slurry is a rubber lined Mag Flowmeter. Mining slurry is too abrasive for coriolis or vortex meter. Transit time U/S will not work with slurry, only clean liquids with no gas bubbles.

Roy

Favorite Field instrument:

1) Plain old thermocouple, for its simplicity and durability.

2) Any of the modern "smart" pressure transmitters with HART.

The long term stability is just fantastic for those of us old enough to remember the quarterly cal routines with the zero and span pots.

The ease of setup via HART is fantastic.

3) Not a field instrument, but I love OPC. Getting the instrument driver out of the HMI software and into the specialty realm of "OPC server" vendors has been fantastic. As good as getting the print driver out of the DOS application and onto the printer manufacturer where it belongs.

Three cheers for OPC.

Carl

My favourite field instrument devices are (skip my latest post):

1. Differential pressure transmitter
Why? It's cheap, easy to install and is applicable to measure flow level and of course, the pressure.
2. RTD temperature transmitter
Why? It's cheap (didn't we love the economics?), it can be calibrated easier than any type of the temperature transmitter and easy to install (although this fellow used to be put in harsh conditions)
3. Universal loop controller
Now why did I choose these devices with all the improvement of the field control system and PLCs? Well, for some low budget factory and not interest of full automation on their plant, these things are considered more effective, and I like the simplicity of the controlling loop (we'll exclude the LCD displayed and shortkeys and complex menu for different vendors).

I love mercury filled level switches, where mercury is filled in a small rectangle type container and this container is put in tilted position... these type of switches are very reliable and fail when its bladder gets ruptured. Otherwise no chance of failure.

Okay, let's see the score boards:
1. Pressure Transmitter (2 quotes)
2. Thermocouple, RTD, Magnetic Flowmeter, Universal LOOP, Mercury Filled Level Switch.

That's the result for round 1, anyone want to change the scores?