Patent GB-801120-A (GB)
Title: Electrical network measuring arrangement with automatically variable attenuator
IPC: H04M3/32
Filed: 1955-02-28
Abstract: 801,120. Measuring attenuation. SKILLMAN & CO., PTY., Ltd., T. S. Feb. 28, 1955 [March 8, 1954; March 31, 1954], No. 5894/55 Class 37. In systems for measuring the gain or loss of transmission lines or elements, a signal received via the apparatus to be tested is rectified and compared with a rectified standard signal from the same or a different source and the signals are automatically brought to equality by the adjustment of an attenuator in the path of either signal by cutting in alternating elements of progressively smaller size. When the insertion of a particular element takes the system past the balance point, this element is disconnected and the next one substituted. In two of several embodiments described, the above operation is performed with test signals of a number of different frequencies in turn. In one of these, if the gain or loss is not within predetermined tolerances which differ for different frequencies, a signal is given and the test is brought to a standstill. In the other system, the actual values of attenuation at all the test frequencies is printed on a tape. The arrangements may be associated with the automatic tape-controlled routining equipment described in Specification 798,571. First system, Figs. 1, 2. On the momentary connection locally or from a distance of points T1, T2, start relay ST pulls up and locks and thereafter a continuously running interrupter energizes relays FP, SP alternately. FP thus delivers impulses to the reverse-drive stepping magnet DM of a uniselector which on its add terminals energizes in successive relays 32P ... 1P which connect up progressively smaller sections of an attenuation network AT. The operations of SP are without effect until the signal in the lower path in Fig. 1 is weaker than that in the path containing the apparatus to be tested. LDC then pulls up and, in consequence, PR which grounds the even terminals in bank DM2. Consequently, when the next step takes the switch to an even position, the most recently operated relay 32P ... 1P is shunted out. LDC and PR then fall back. The next step connects up a smaller section of the attenuator and the test proceeds as before. The connected sections are shown by a lamp indicator L32 ... L1. On its final terminals, the switch shunts out ST and stops. When a new test is to be made, the circuit is cleared by a momentary disconnection of battery by the release key RK or by a disturb release key connected to points T3 and T4 with the strap removed. Modified lamp indicator. In Fig. 3 (not shown) an arrangement is illustrated for showing the total attenuation (as distinct from the values of the connected sections in a case in which the sections have the values 40, 20, 10, 3, 3, 2 and 1 decibels. Second system, Figs. 4 and 5. This is the same as the first system except that it is adapted to a situation in which the circuit or element tested may have a gain or a loss. If, after the insertion of the whole pad in the balancing branch by relays 32P ... 1P, the relay LDC fails to operate, a circuit is made for TFR which locks and transposes the connections so that the element or path being tested is connected to the differential relay LDC via the adjustable attenuator and the signal source is connected direct. The test is then repeated over the second half of the bank of switch DM. Loss and gain lamps LL, GL indicate which half of the bank is being used. Third system, Figs. 6 to 9. Tests as previously described are repeated with a number of different signal frequencies. Each path contains an adjustable attenuator A, B set to a value depending on the tolerable deviation at the frequency being used from the value at a standard frequency. On the operation of key STK, relays STR, SSR pull up in turn and sequence switch SW is driven to its second terminals. Relay 8R operates and connects up an oscillator 8 of say 800 c.p.s. and apparatus as described in the preceding paragraphs controls attenuator AT to balance the two paths. During the time, relay ST in the balancing equipment prevents further movement of SW but when balance is achieved and ST falls back, SW moves to its next position in which LCA is operated. If the attenuation figure is not within the required tolerance LCB pulls up and releases STR to prevent further stepping of the switch. If, however, the apparatus passes the test, the switch moves on and a new oscillator is connected up by 4R. At the same time one of the relays ¢B ... 2B is energized to insert an attenuator section, depending on the tolerance at the new frequency, into the B path. This should cause the immediate operation of LDC whereupon LMR pulls up and energizes STR and SW takes another step. In this position one of the relays ¢A ... 2A depending on the tolerance in the opposite sense at the same frequency connects a pad section on the A path. If the device passes the test, LDC is not energized, LMR falls and STR is re-operated to enable the switch SW to step on and initiate a repetition of the tests at a new frequency. Failure to pass the test at any point results in the failure of LMR to operate when it should or in its operation when it should not. As a result, the sequence switch cannot step on and FR lights a " fault " lamp FL. If the automatic balancing equipment indicates a gain rather than a loss, relay TFR makes the necessary transposition in the circuits controlled by LMR. If the circuit passes the test at all frequencies TCR pulls up, releases the automatic balancing equipment and relay SSR and switch SW thereupon homes by self-interruption. The equipment may be modified as indicated by the connections shown dotted so that TCR is not operated on the first trip of the switch SW. COR then operates and locks and may initiate changes in the apparatus under test which is then tested again. Assuming that this test also is completely successful, TCR pulls up on the second trip of SW and releases COR. Fourth system, Figs. 10 ... 12, in which attenuation at various frequencies is measured and recorded. The successive connection or tuning of the oscillators is controlled by a sequence switch A, Fig. 11. On the operation of a starting key STK, this switch moves to its second terminals and 8R connects up the 800- cycle oscillator. ATS sends a starting signal to automatic balancing equipment AT which is then set as previously described and at the completion of the operation sends an impulse to move switch A to its third terminals on which PT is operated to control the printing of the value set up in AT. PT, on operating, steps a printer sequence switch B on to its second terminals in which a selection of printer control magnets PRA, PRB, PRD, PRE is operated in accordance with the condition of the relays 8R ... 32R which determine the oscillator frequency. The switch then steps on uniformly to the end of the bank under control of the selfinterrupting slow-operating relay PFR. PRF also energizes the print magnet. Similar actions occur in subsequent positions of B to print say " 800 c.p.s." A + sign is printed if TFR is actuated in AT and a - sign if it is not. Subsequently the value of the inserted attenuation is printed in accordance with the pad-controlling relays. In the final position, PRZ steps on switch A and PT falls to drive switch B to its normal position. In position 4 of A, a new frequency is connected up and BTS, operates slow-to-operate relay BTT to clear and then start the balancing action of a second attenuator AT<SP>1</SP>. When the latter reaches,its last terminals it steps on switch A whereupon PT operates again and this time prints the new frequency and attenuation values. After the preliminary test at 800 cycles 8R falls back and thereafter if TFR<SP>1</SP> (not shown) in AT<SP>1</SP> operates when TFR is not operated TFS pulls up and transposes upper and lower paths between the two attenuators. Construction of printer. A quadrant SG carrying the characters is moved behind a printing gate in accordance with the combined effect of magnets PRA ... PRE. The printing hammer PH is actuated by a magnet PM and also actuates the tape feed mechanism.