Don't act on impulses, use good sensors
11 Apr 2018
The world has moved on and so has the technology at our disposal. Why then, asks Ken Roberts, do so many in the process industry seek to make their job more difficult?
Why do so many plants insist on using the same old instrument installation methods they did when most instruments were huff and puff and less reliable than a 1970’s Austin ‘All Agro’?
I’ve made a living out of process automation for nearly 50 years. It makes me cringe that I still see DP cells beautifully and very expensively installed in places a long way from where the measurement is to be made. Connecting the instrument to the process by long thin tubes and complicated manifolds is expensive and asking for troublesome blockages.
Of course there are times when that is the best way to install a delicate instrument but not when the instrument itself is tough as nails and reliable beyond our microprocessor based expectations.
When the stuff you’re going to measure is truly horrible, why would you want to encourage it to make life even more difficult for you? Allowing it to sit undisturbed by any flow in little lines while it’s just itching to quietly go solid on you is just crazy.
When the stuff you’re going to measure is truly horrible, why would you want to encourage it to make life even more difficult?
If it’s “there” where I want to know what the pressure is, then put the measuring sensor there – simple.
OK so there might be some issues. Shutting the plant down to get at the instrument if the worst happens is a big one. Instruments designed to connect straight into the process directly or though valves will overcome that problem.
At the simplest, just shove the sensor through a little ball valve straight into the process. If that’s not practical for a particular installation, there are valves that allow safe installation and isolation up to 40 bar. These have been used by some of the major manufacturers for many years, mainly on Ph probes.
A ball valve based complete installation and service valve, PASVE™ puts any sensor with a G1 or M45x2 connection right inside the process and solves the problem of safe access for maintenance while the process is live. PAVE™ can even enable flushing flow to clean sensitive sensors like Ph electrodes or introduce calibration fluids, either, automatically, if needed.
Sending some poor instrument mechanic out to unblock them isn’t the only way to deal with blocked impulse lines. There’s an Australian crew who make an automated rodding device to help with the issue. Others use flushing systems - of varying complexity or expensive and delicate chemical seals in an attempt to avoid the plugging problem.
In an age when most instruments can sense and alarm when a blocked connection is detected, are we forgetting that proper engineering provides real solutions to problems and not just ways to manage the results a problem.
Come on process control world - wake up – discover what the Pulp and Paper industry worked out ages ago; install sensors right into the process through PASVE™ or other suitable valves and only use impulse lines and capillaries when you can’t avoid them.
Ken Roberts is manager, Satron Instruments
