Patent GB-647360-A (GB)
Title: Improvements in or relating to measuring arrangements
Inventor: BAKER GEORGE THOMAS
IPC: G01R27/02
Filed: 1948-01-30
Abstract: 647,360. Capacitance and resistance measuring. AUTOMATIC TELEPHONES & ELECTRIC CO., Ltd. Jan. 30, 1948, No. 2802. [Class 37] According to one aspect of the invention the component to be measured forms part of a resistance-capacity combination which controls a relaxation circuit which is transferred to its unstable condition to discharge the condenser, and the time taken for the relaxation circuit to revert is measured and is related to the value of the resistance or capacitance. According to another aspect of the invention the resistancecapacity combination opens a gate circuit when the capacitance is discharged and closes the gate when the charge on the capacitance reaches a predetermined value, the gate circuit passing impulses which are counted as a measure of the time and thus of the value of the resistance or capacitance. According to yet another aspect of the invention the time taken for the capacitance of an R.C. combination to charge or discharge from one predetermined value to another is compared with two time intervals to determine whether the resistance or the capacitance lies within limiting values. The condenser C1, Fig. 2, to bemeasured is connected to a pair of backcoupled valves V1, V2 of which normally V2 is conducting, since its grid is earthed over diode V3. As a consequence the potential at A2 is too low to allow valve V4 to conduct. When contacts BR1 close, a positive pulse is applied to the grid of valve V1 to render it conducting and make valve V2 non-conducting. The diode V3 ceases to conduct and condenser C1 1 discharges through resistance R2. The rise in potential at A2 when valve V2 becomes non-conducting renders valve V4 conducting to allow pulses from sources to pass to the counting circuit CC. When the condenser has discharged to a predetermined level, valve V1 ceases to conduct, valve V2 thereupon conducts to prevent valve V4 conducting, and the counter CC registers a number proportional to the time taken by the condenser to discharge which is related to the value of the condenser. The cycle may be made repetitive ; contact KA being closed actuates relay GR which operates relay AR which resets the counter CC over contacts AR2 and de-energizes relay BR over contacts AR1 to actuate the starting key BR1 ; if GR is a galvanometer type of relay, contacts GR1 will be opened and closed in accordance with the mechanical period of oscillation and relays AR, GR, BR will be actuated in unison therewith. A circuit adapted to indicate whether the condenser lies within defined limits is shown in Fig. 4. A generator S12 supplies sequences of twelve impulses of which the first is applied to transpose valve V22, V23 and start the condenser C26 under test discharging ; the ninth and eleventh impulses from S12 are applied to transpose valves V20, V21 so that between these impulses valve V24 is capable of conducting any impulse applied from valves V22, V23; a condenser of normal value is such as to discharge to the point where valves V22, V23 change over when the tenth pulse occurs, so that if the condenser under test is within Œ 10 per cent of this value, the valves V22, V23 change over between the ninth and eleventh pulses and valve V24 conducts to change over valves V25, V26, and light the neon lamp NT. If the condenser is outside these limits, neon tube NT does not ignite. The arrangement of Fig. 6 is adapted to indicate whether the condenser C35 is below, above or within certain limits. When contact BR1 is closed, the three sets of valve pairs SSN, SSo, SSP are transposed. SSN and SSP switch back at minimum and maximum times respectively, while SSo switches back at a time determined by condenser C35. If the condenser lies within the predetermined limits, SSN reverts first to cause the valve pair SIA to transpose and light neon lamp NTA ; SSo then reverts to cause SIA to revert and extinguish the lamp NTA and the reversion of SIA passes a pulse to SIB to cause transposition of conduction and lighting of lamp NTB ; finally when SSP reverts, the valve pair SIB revert to extinguish lamp NTB, and cause transposition of conduction of valve pair SIc to light lamp NTC, which remains lighted to indicate that the condenser is within the predetermined limits. If SSo reverts before SSN, it is without effect on SIA, so that when SSN reverts, SIA transposes to light NTA; the subsequent transposition of SSP is without effect on SIB and consequently lamp NTC is not lighted. Thus, NTA continues to glow and lamps NTB, NTC do not ignite to indicate that the condenser C35 is below the limit. Should it be above the limit, SSN transposes first to light NTA ; SSP next transposes, but is without effect on SIB so that lamps NTB and NTC are left unlit ; finally, SSo transposes to cause SIA to revert, extinguish lamp NTA and light lamp NTB which continues to glow to indicate that the condenser is above the limit. If the condenser is maintained constant, the series resistance can be measured.