This could take current or voltage inputs from many remote transmitters, 4-20mA or 0-1 V Inputs. Then it would display the calibrated value in a LED display. The Zone number was a digital display. This serves as a monitor of process values. It had a analog output with a digital channel byte-word output for interface with other instruments.
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The one above was also made at TMPL, it is a Psophometer which was a true RMS auto-ranging AC dB level meter with weighted filters. The weighted filter has to resemble the audio response curve of the ear. With a built in signal generator in dB settings it becomes a Transmission Measuring Set. This was in the eighties, it is similar to this Transmission Measuring Set from Aplab, this was the only relevant link i got. I also remember that aplab also had submitted a sample of a bigger unit then. Then some nice European units also were being evaluated by the buyer.
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Psophometer - Wikipedia, the free encyclopedia. I learnt some basic instrumentation when i worked on above Instrument, Mr. Ravi Rao the Manager in Trans Marketing Pvt. Ltd. gave that opportunity. TMPL as it was known decades back was in Service and Sales of many Brands like Racal Dana, Genrad, Data I/O and Electronic Production Machinery.
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