Analog v. Digital: Electro-pneumatic positioner (i/p)...

Speaking from a totally biased view point analogue is the real world stuff.... its difficult to design with and that's why people have been forced into thinking that digital is better...

The computer age has seen masses of designers overwhelmed by the signals from this analogue world... They prefer a 'nice' signal which has only two values either on or off.... to talk to them about a signal that has an approaching infinite number of states, sends them in to a blind panic!!

Their minds have been programmed by their education into thinking that all solutions are either on or off.... the real world throws them, until they can bury themselves behind a comfortable warm glow of a computer monitor!!

Ahhh they cry, when approached by an analogue problem, we have a simulation software package that can solve that!..... alas, they are anware, or unwilling to consider the fact that the software simulation package has to be designed by an analogue engineer for it to work....

The simulation packages i've tested are rubbish, unless you want to spend thousands on one that will tell you a perfectly good design that's been in production for eons is not feasible!!!

So although I'm an analogue engineer and proud of it.... I'm not really biased, I'm just furious that people should even contemplate using digital, micro, computer, software designs to do a simple analogue design!!

John (blessed in the art of analogue design, & modest too)

I think there is no big problem between analog and digital, and for the best positioner is relative. I think I can use all positioner, no matter with the brand.

I/P, A/D, V/P, RDT, LDT, LVDT, whatever, The basis for comparison is the Jordan drive.

4-20 madc input signal

initially comparatively expensive, precisely accurate, repeatable, reliable, linear output, although not intentional it may function accurately submerged

Having come initially form a pneumatic control background and then moving into digital control later on I tend to agree with everything that Electroman and Cornstoves have said. However to be fair there are two sides to the argument.

Firstly and digital representation of an analogue signal is only an approximation of the real world environment. However having said that a 16 bit digital signal approximates the input to within ±0.0008% which in nearly all cases will be many times less than the sort of signal to noise ratio you can achieve with and analogue signal.

For a simple feed back loop converting an analogue signal to digital processing it then converting it back to an analogue output can be a disaster. Not only dose it involve more components but every time you convert a signal you decrease the signal to noise ratio.

When you start to talk of multiple complex interacting control loops then digital starts to come into it own. For example imagine that you have a skyscraper that has several hundred small air conditioning units all linked to a central plant room that supplies cold and hot water. You could control each of the units individually but if you wanted to be able to modify the individual loops to enable the most energy efficient operation of the system as a whole then digital would be the way to go.

To sum it up it depends on what you are trying to do and the complexity of the process you are trying to control. For really complex systems digital may be the only viable solution especially when you are doing thing like differential and integral control. However don't just assume that you need to use digital all the time as analogue may be a simpler and cheaper solution.

As for the brand then there is a huge variation in the quality. Only stick with reputable manufacturers that have good technical support and spare parts back up. Also be careful of forgeries and copies there is a lot of cheap crap out there so if possible deal directly with the manufacturer.

Masu, what's the source of this quote?

"We the unwilling, lead by the unqualified, have been doing the unbelievable for so long with so little that we now feel confident attempting the impossible with nothing."

I love it!

www.thefreedomfarm.com

I wish I knew. I just remember seeing it written on the toilet wall where I worked and thought it was worth remembering. If you do a search on it you will find a couple of hundred occurrences of it on the net. Feel free to use it and If you ever find out where it comes from I would be interested to know.

Where is this toilet wall?

I need to know just in case I cite it in a peer-reviewed journal or something.

Thanks!

www.thefreedomfarm.com

Consider Beck Drives

If a pneumatic supply is readily available, redundant electrical power is not available, and loss of service is a concern, consider pneumatics. The pneumatic supply usually remains charged for some time after loss of electrical power or grid power blackout.

An air dryer, sloped pneumatic lines, and water traps must be used to prevent loss of pneumatics during freezing weather.