TY - JOUR
AU - Levitt, Seymour H.
AB - Design of a High Impedance Vacuum Tube Voltmeter for Use in the Radioisotope Laboratory 1 Carl R. Bogardus Jr. , M.D. and Seymour H. Levitt , M.D. Excerpt A reliable, yet simple, voltage-measuring device was needed in our Isotope Laboratory (University of Oklahoma Medical Center). On many occasions we have had to switch a scintillation or Geiger head from one counting instrument to another because of breakdown or alternative application. A high-voltage voltmeter is useful in making certain one does not exceed tube-voltage ratings when peaking in on different instruments. Most scalers and ratemeters have a series of dropping resistors in the Geiger input circuit, which will give considerable voltage drop if loaded to any degree by a low-resistance external voltage-measuring device such as a conventional voltmeter. The instrument constructed has a D.C. input resistance of 110 million ohms, so negligible drain is placed on the system to be measured. We have found it quite useful in checking high voltage on malfunctioning equipment, as well as in the repair of equipment with disabled high-voltage power supplies. Two voltage ranges are provided, and the meter may be used with either positive or negative output power supplies. Multiple coaxial connector inputs are employed. This enables us to connect the phototube to one terminal and the high-voltage power supply to another. With this arrangement the unit is very versatile and may be used on any machine in the laboratory without special wiring or complex cable connections. Many of the major components for such an instrument are readily available as surplus parts in the average isotope laboratory. This meter was not designed for extreme accuracy but rather for stability of reading and daily reproducibility. We found, however, that after final calibration it exceeded our original expectations. Our final calibration is found to be linear with the calibrating power supply within plus or minus 10 volts at any voltage. This gives an overall error of plus or minus 0.7 per cent full scale, or far closer than the scale itself can be read under normal conditions. The basic design is a standard vacuum tube voltmeter circuit with a high impedance input (Fig. 1). The meter used in this instrument was salvaged from an older piece of equipment. The original numbers were removed, the scale divisions were retained, and a new dual voltage scale was lettered on the face. Two zero controls are used. (R18) gives a range of plus or minus 1/2 scale. The fine zero (R19) on the front panel is operable over a range of plus or minus 1/20 scale. A push-button switch (S1) is used to ground the signal voltage developed across the input resistance. This gives a zero signal on the grids and permits one to check and adjust the zero setting when high voltage is present. The unit was calibrated against a very accurate high-voltage power supply. We were able to calibrate the meter as accurately as it could be read. The instrument described has been in continuous use in our laboratory now for well over one year and has proved reliable and extremely useful.
TI - Design of a High Impedance Vacuum Tube Voltmeter for Use in the Radioisotope Laboratory
JF - Radiology
DO - 10.1148/87.2.357
DA - 1966-08-01
UR - https://www.deepdyve.com/lp/radiological-society-of-north-america-inc/design-of-a-high-impedance-vacuum-tube-voltmeter-for-use-in-the-1bzJZFB0os
SP - 357
VL - 87
IS - 2
DP - DeepDyve
ER -