INSTRUMENTATION BY
R A L P H
H.
M U L L E R
New Logic-Assisted DC Potentiometric Voltmeter
Τ" 1 H E J A M E S C
BIDDLE C O . of P l y m -
*- outh Meeting, Pa., 19462, has de veloped a series of production-line test instruments which approach the accu racy of the primary standard labora tory potentiometer and the func tional simplicity of the digital volt meter, in a form suitable for use by nontechnical personnel. The instrument principle, designated the Mentor, is a decision-free, five-place measuring tech nique which fills a distinctive need and speeds u p testing operations in the lab oratory or in production tests. A typi cal five-place reading takes less than 10 seconds, on the average, 7 seconds. Also, if drift occurs in the source under measurement, wherein the last two digits require correction, less time is required for correction. As an example, the Model 404 do voltmeter is illustrated in Figure 1.
The panel contains seven display win dows, the first for parameter (in this case dc volts), illuminated when the instrument is turned on; the second for polarity, and the remaining five for the digital readout. With each of the latter six, and with the range indicator, is associated a switch and two arrows to indicate whether the switch should be pushed up or down. When an un known voltage is applied to the instru ment's input terminals, the logic first interprets the range and polarity of the output of the null detecting amplifier. If either or both are incorrectly set, arrows indicate, one at a time, how the switches should be readjusted. If they happen to be set correctly, the logic proceeds to the next step. Decimal point location is indicated by lamps. When polarity and range are both set correctly, an arrow is illuminated
at the first of the five digital readout windows. When the switch is properly adjusted, and the window lit, the ar row goes out and the process is re peated at each of the next four settings, until the complete reading, accurate to 100 ppm, is displayed. Only one of the 14 indicating arrows lights u p at a time; the operator is never in doubt about which adjustment to make next. No window is illuminated unless the associated switch is correctly set. The reading is correct or there is no reading. If 'the input drifts, readout of the affected decades is extinguished and the arrows backtrack to the point where resetting must begin. The Men tor instrument may also be preset to any desired voltage value to check on the setting of an adjustable input. (Continued
on page 150 A)
Figure 1. Model 404 dc voltmeter made by James C. Biddle Co.
-Circle No. 35 on Readers' Service Card VOL. 4 0 , NO. 2, FEBRUARY 1968
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149 A
INSTRUMENTATION
Ace Scientific Burrell W. H. Curtin Matheson Preiser SGA Ε. Η. Sargent
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t
all will be featuring the latest Corning advances in labware and scientific instruments at the Pittsburgh Conference. W e invite you to visit their booths and catch up on the latest. Catch up on Corning.
CORNING LABORATORY
PRODUCTS
Circle No. 232 on Readers' Service Carfl
150 A
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ANALYTICAL CHEMISTRY
Γ =,
