John P Morin

US Patent:

41639715, Aug 7, 1979

Filed:

May 5, 1975

Appl. No.:

5/574446

Inventors:

John O. Morin - Bedford MA
Joseph R. Mini - Abington MA

Assignee:

Sigma Instruments Inc. - Braintree MA

International Classification:

G01D 700

US Classification:

340754

Abstract:

In the system disclosed a driving circuit repeatedly scans along a plurality of aligned electrodes in an enclosure filled with ionizable gas, by sequentially grounding the aligned electrodes and repeating the process cyclically. Within each cycle, a pulse width modulator energizes an anode opposite the electrodes for a period of time corresponding to an input value. Sequential glow discharges thus occur between the cathodes and the anode over a portion of the anode length. The discharges occur with sufficient rapidity so that they are observed as an illuminated portion of a bar formed by the electrodes. A second set of electrodes is scanned and an opposing anode energized to produce two illuminated bands separated from each other. Desired upper and lower set point limits for the input quantity determine the lengths of the bands and the separation between them. According to one embodiment, the separate bands are initiated from opposite ends of the bar formed by the electrode alignment with suitable reset cathodes.