| 摘要 |
A digital voltmeter which does not require comparison of the unknown voltage with a reference voltage and, which, during periods of no input voltage, does not consume energy. The voltmeter of the invention essentially is a constant current device wherein resistance from one or more resistor banks is added or deleted in stepwise fashion in series with a sensing relay coil, this series circuit being connected directly across the unknown voltage terminal. This voltmeter is adapted to measure voltages accurately to within a minimum digital increment of voltage which depends upon the sensitivity of the sensing relay coil. The current-sensing relay coil has a current threshold equal to the ratio of the minimum increment of voltage to be measured and the resistance of said sensing relay coil. The sensing relay includes a contact which moves back and forth between two positions, depending upon whether the current in the aforesaid circuit is greater than or less than a predetermined threshold value. The amount of resistance in the current path is partially dependent upon the position of said contact and will be governed by the magnitude of the unknown voltage. The digital voltmeter also includes a plurality of banks of relays associated with each bank of resistors and indicating means associated with said relay banks. The magnitude of each of the resistors in the various resistor banks is digitally related to the magnitude of the resistors in the other banks. There are n banks of resistors, where n is the number of digits of the voltage to be measured. The magnitude of all resistors of a given resistor bank is equal and the magnitude of the resistors of the successive resistor banks, representing successively lower significant digits, decreases by a factor of 10. The resistance of the sensing relay coil must be equal to or less than one-tenth of the value of the resistance of each resistor of the resistor bank corresponding to the least significant digit of the voltage to be measured in order to insure accurate measurement of voltage. The voltmeter also includes a switch which sequentially applies a direct current voltage to the various relays of a corresponding relay bank when the contact of the current sensing relay is in one of its two positions. As each relay of the various b
|
