By Dr. Otto Fest
Pictured is a “loop-powered” tricolor bargraph digital meter with on-off alarms, isolated serial I/O, isolated 4-20 mA retransmission and auto-loop failure detection alarm.
To your mind, what’s more important — what’s more epoch-making, if you will — “individual genius” or “social intelligence?”
The answer is that “no man is an island.” Human evolutionary success is first and foremost based on social organization and the ability to share experiences and knowledge.
The greatest innovators didn’t operate in a void. Julius Caesar, for example, had an army behind him when he crossed first the Rhine River and then the English Channel, bringing civilization to Germany and Britain.
As to modern technology, whether its Thomas Edison and the light bulb; Alexander Graham Bell and the telephone; Nikola Tesla with the Tesla coil, AC power and fluorescent light bulb; or Schottky and Schockley and their work with semiconductors; just a peek under the covers shows their inventions were most often the culmination of other incremental discoveries and inventions or issued from highly collaborative environments.
At this point it gets personal. My first experience with electricity came with a visit to Mexico City from the farm where I was raised, under kerosene lamplights, during World War II. It was the beginning of a lifelong love affair.
Lifetimes of work
When I started OTEK Corp. in 1974 I wondered about the wasted energy in current loops, used only to transmit a signal over two wires to end up at an analog meter, valve or A/D converter controlling a process. This seemed a waste of both energy and information to me.
At this point in the 1970s (a wonderful decade) many different individuals, both well known and anonymous, had contributed to the advances made since World War II in electronics use for process control. Just in this particular instance, for example, someone developed the first liquid crystal displays (LCDs) and someone else the analog-to-digital (A/D) converter. My contribution was to develop the industry’s first loop-powered digital panel meter (DPM).
Up until then, current-loop instrumentation used the existing quiescent energy of the current loop (typically 24Vdc and 4-20mA) to operate. If analog, to move its pointer; if motor, to control its speed; if stepper or valve, to control its position; if electronic display, to show the value of the current flowing in it. But anything other than the actual display of the measured value had to be externally powered.
The next step was crucial. Someone bought my LCD DPM, added it to their product, and then sold that solution to someone else, who used it to rectify a problem. It’s called capitalism, and in some ways resembles a closed-loop circuit!
Our new technology requires less than 1% energy of comparable powered units (~10-50mW versus 1-10W) to operate its LED, multicolor bar, digital display; communicate serially with supervisory equipment; enable alarms; and retransmit current loops for monitoring and control or detect incoming loop or signal failure.
All isolated from the incoming loop and all loop powered!
The story continues
Now once our loop-powered “Powerless DPM” was introduced, I started wondering how to use that minute amount of energy — only 4-20mA — to power other devices without affecting its accuracy. So over the years, we developed LCD and LED DPMs, on-off and proportional controllers, radio-frequency transmitters, radiation monitors and LCD bargraph meters, all powered by the current loop.
But our goal always was to develop a 100% loop-powered automatic tricolor, HMI-compliant, LED bargraph to complement our HiQ-powered version.
Just last year someone else improved the LED technology and someone else produced a nanotechnology ultra-low power microcontroller. Thus, 40 years following introduction of the industry’s first loop-powered DPM, we introduced the first fully automatic tricolor bargraph digital meter with on-off alarms, isolated serial I/O (USB or RS-485), isolated 4-20m Aretransmission (externally loop-powered) and auto loop failure detection/alarm.
I am often asked, how can you claim loop-failure alarm when there is no current flowing in the loop?
To which I reply: “It’s simple, when the loop is normal we store energy. When we detect the loop dropping below 4mA we send a distress message via the serial loop to the user, turn off the bar graph and flash the display ‘LOOP FAIL’ until the stored energy bleeds – typically in about 20 seconds.”
The four most important technical features of the LPD series include the following:
• For nuclear customers or when replacing analog meters, no rewiring
• Serial communications for DCS/SCADA/ETHERNET
• Automatic tricolor bar-digital display (HMI)
• Loop failure detection
All thanks to social intelligence and the magic of the 4-20mA current loop (only 10 to 50mW @ 4-20mA)!
The most important factor that users overlook is the amount of quiescent voltage (EMF) left over after all loads are added, creating inaccuracies and failure.
Dr. Otto Fest is President and Founder of OTEK Corporation. Prior to founding OTEK he worked in the Apollo program from 1967 to 1972. He can be reached at 520-748-7900 or firstname.lastname@example.org.
OTEK Corp. of Tucson, Ariz., founded in 1974, manufactures to several Mil-Spec, Class 1E, RTCA-160 and IEEE standards. The company holds several patents in loop-powered and AC signal-powered technologies.