Patent GB-460737-A (GB)
Title: A circuit arrangement for measuring short time intervals
IPC: H03K17/288
Filed: 1935-12-31
Abstract: 460,737. Pressure meters. JORGENSEN, M. O., and WEIBEL, M. P. Dec. 31, 1935, No. 36093. Convention date, Jan. 2. [Class 37] In a circuit arrangement for measuring short time intervals of the kind in which the charge on a condenser which is partially charged or discharged through a resistance throughout the time interval to be measured is determined, this quantity is obtained by measuring the difference between a known fraction of the voltage supply tapped by means of a potentiometer and the voltage across the condenser. In the case of a condenser C, Fig. 4, which is charged from the supply B through the resistance R when switch 2 is closed and switch 1 is open, a potentiometer D is arranged across the supply B and when the doublepole switch O is in the full line position, a contact s1 which may be fixed or adjustable connects the grid G of a valve A to a point on the potentiometer, while the filament of the valve is connected to the point k3. This applies to the grid G a voltage which is the difference between a known fraction of the voltage of the supply B. and the voltage across the condenser, and this is determined by means of the current measuring device M and the known relationship between the plate current and grid voltage of the valve A. If the latter is not known, the switch O may be moved to the dotted line position, when a fraction of the voltage B is applied between the grid and the filament which is adjusted by means of the slider s2 until the reading of the device M is the same as before and by this means the voltage between the points s1, k3 is found as a fraction of voltage B, which therefore has not to be measured. If desired, the contact s2 may be dispensed with, contact s1, only being employed. In a modification, a ballistic galvanometer is employed which, on the closing of a switch either manually or by the valve and relay device of Fig. 6, measures the voltage between the points s1, k3 and in this case the galvanometer is calibrated by applying a known fraction of the supply voltage thereto or by charging the condenser C to a known fraction of the voltage and discharging this through the galvanometer. When using the arrangement for measuring the time of flight of bullets for example, long connecting leads L1, L2, L3 may be necessary and in order to avoid insulation troubles, one or more relays may be inserted in the leads for operating contacts in one or more of the leads. In the arrangement shown in Fig. 6 which is to be used with the measuring device of Fig. 4, a contact 4 is provided in the circuit of the condenser C and is also included in the grid to filament circuit of a valve A1 ; in the plate to filament circuit of the valve is a relay coil Sp which serves to close the contact 4 against a spring F. In use, after closing contact 2, contact 4 is closed by hand or by closing a second contact shortcircuiting contact 4, when sufficient current flows in the plate circuit to energize the coil Sp and maintain the contact 4 closed. Upon opening the contact 2, at the-end of the interval to be measured, the grid G1, has a negative bias as the condenser is never charged to the full voltage of the supply B, so that the relay coil is de-energized and the contact 4 is broken.