Patent GB-875143-A (GB)
Title: Improvements in or relating to apparatus for measuring voltage
Inventor: BOWES ROBIN COLIN
IPC: H03M1/00
Filed: 1957-03-14
Abstract: 875,143. Electric selective signalling systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 11, 1958 [March 14, 1957], No. 8446/57. Class 40 (1).  Apparatus for measuring voltage comprises a comparison circuit receiving an input and a reference voltage; means for changing the latter by progressively smaller steps in binary sequence wherein each of a plurality of connecting means is operable to. connect or disconnect a different step of reference voltage and a pulse signal source applies pulse signals to inputs of the connecting means which ensure their operation to connect the steps in binary sequence; the arrangement being such that each pulse signal is fed to a gated path as well as to its 'given connecting means, the gated path gives controlled access to the preceding connecting means in the binary sequence to disconnect the corresponding voltage step; and the comparison circuit controls the gates of the paths so that upon the occurrence of a pulse signal a voltage step connected in response to the succeeding pulse signal remains connected or is disconnected according to the result of a comparison between the input and reference voltages with the voltage step connected; while means are associated with the voltage sources for indicating which steps of reference voltage remain connected after completion of the binary sequence, whereby the magnitude of the input voltage is indicated in terms of a binary number. In Fig. 1 an input voltage is applied to fixed contact 2 of a chopper whose fixed contact 3 is fed from a binary reference voltage source and whose moving contact operated by drive 9 from control multivibrator 10 feeds comparison differentiating circuit 6 alternately with input and reference voltages to produce negative or positive pulses as the input is greater or less than the reference voltage, which energize limiting amplifier 7 (Fig. 3, not shown) to trigger the overshoot inhibited generator 8 (Fig. 2, not shown) on positive pulses to generate long gating pulses. Multivibrator 10 drives pulse separator 12 through delay circuit 11 to produce for every train of 11 delayed multivibrator pulses a first output pulse at PS1, a second at PS2, a third at PS3, up to an eleventh at PS11 of which outputs PS1 to PS10 trigger respective bi-stable circuits BS1 to BS10 to sequentially operate relays A to J whose contacts A1 to J1 connect graduated resistors 13 to 22 respectively in series with a stabilized voltage source 23 to fixed contact 3, which is earthed over resistor FBR, so that a binary coded voltage is applied to the contact in successive increments each of which is half the magnitude of the preceding increment. In operation a start signal on terminal 24 trips multivibrator 10 and clears all the bi-stable circuits BS1-BS10 to release relays A to J so that no reference voltage is developed and source 23 is earthed over resistors 13 to 22. The first operative edge of the multivibrator output triggers drive 9 to change over contact 5 from 3 to 2, and after a delay a pulse at PS1 operates bi-stable circuit BS1 and relay A to connect to contact 3 a reference voltage (1) determined by resistance 13. The next operative edge of the multivibrator output triggers chopper drive 9 to change over contact 5 from 2 to 3. The third operative edge triggers chopper drive 9 to change over contact 5 from 3 to 2, the input and reference voltages are compared and a positive or negative pulse is supplied by differentiating circuit 6 through amplifier 7 to gate pulse generator 8 which is inoperative when input is greater than reference voltage, but operates when reference is greater than input voltage to open biased diode gates 26 (Fig. 2, not shown) between the respective outputs PS2 to PS11 of the pulse separator 12 and the bi-stable circuits BS1 to BS10 to route separated pulses to the respective bi-stable transistor multivibrator circuits BS1 to BS10 (Fig. 2, not shown) corresponding to the preceding output PS1 to PS10. The third operative edge also produces with delay a pulse at output PS2 which operates bi-stable circuit BS2 and relay B. Since gate 26 is closed, the preceding bistable circuit BS1 is not pulsed by PS2, and relay A remains operative. Resistor 14 is connected over B to contact 3 to add a binary increment (¢) of reference voltage determined by resistor 14. On the fourth operative edge of the multivibrator output, chopper drive 9 changes over contact 5 from 2 to 3, and on the fifth operative edge, contact 5 changes back so that a further comparison is made between reference and input voltages. If the former is now assumed to be greater than the latter, gate pulse generator 8 is positively triggered to apply a long pulse to gates 26, which open and in particular connect the next pulse separator PS3 output to the preceding bi-stable circuit BS2. Thus when a delayed pulse corresponding to the fifth operative edge appears at output PS3, gates 26 are open and bi-stable circuit BS3 is pulsed to operate relay C, while bistable circuit BS2 is also pulsed to release relay B. The increment of reference voltage added on operation of relay B is removed and operation of relay C connects through C 1  a resistor 15 through which a smaller () binary increment of voltage is added. These comparisons between input and reference voltages to determine whether or not an added binary increment should remain continues as successive oddnumbered operative edges are generated by multivibrator 10 originate successive pulses in outputs PS4 to PS11 of pulse separator 12 each of which add a binary increment and initiate decision as to whether the preceding increment should remain or be removed. The magnitude of the input voltage is determined in successive approximations as successive digits of a binary coded number represented by the record contacts A2 to J2 of relays A to J. The start signal applied over terminal 24 initiates the pulse separator 12 and multivibrator 10 to generate 11 pulses or 22 operative edges so that 11 output pulses corresponding to odd-numbered edges are produced by generator 12 in sequence of one per output PS1 to 11, so that on each cycle of operation, the input voltage is measured to 10 binary places. A time serial output may be obtained from the positively and negatively pulsed output of amplifier 7 according as the added increment of reference voltage is to be added or removed by means controlled by multivibrator 10 for selecting pulses corresponding only to comparisons made on the 3rd, 5th, 7th, &c., operative edges of the multivibrator pulses.