Patent GB-1424646-A (GB)
Title: Survey recorders
IPC: G01D9/28
Filed: 1974-02-04
Abstract: 1424646 Recording apparatus; photo-electric apparatus SANGAMO ELECTRIC CO 4 Feb 1974 [19 April 1973] 04968/74 Headings G1A and G1J A recorder in which data from a meter M and time information are recorded on parallel tracks of a magnetic tape includes a timer SW1 to provide time reference signals at predetermined intervals of operation of the meter, a time record circuit 15  including a recording head TH (98), a control circuit 127 for the time record circuit 15 including a power sensing circuit 125 for detecting the presence of power to the meter M and interruption of such power for more than a predetermined period, and logic circuits 134, 136, 153, 154 connected to the power sensing circuit and the timer to control the time record circuit to record a distinctive pulse pattern on the time information track to identify a detected power interruption. As shown, the recorder includes a watt-hour meter M measuring the power used by a consumer, the same A.C. power supply powering a synchronous motor 27 driving the tape drive 20 of the recorder and a cam 26 of the timer SW1, and providing, via a transformer 29 and rectifier 32, a 12.5 volt D.C. supply 38, 49 to the recorder  circuits. Data channel. Light from a light-emitting diode 40 is reflected from the disc 10 of the meter M on to a photo-transistor 41, causing a Schmitt trigger circuit 64 to supply a logic 1 signal to a dividing circuit 84. A dark zone (11), Fig. 1a (not shown) on the disc reduces the reflected light for a fraction of each revolution of the disc, the Schmitt trigger circuit supplying a logic 0 signal during this period. The divider circuit 84 counts only changes from logic I to logic 0, i.e. one count per revolution of disc 10. Divider circuit 84 is programmable to provide a change in pulse output for each 1, 2, 4 or 8 revolutions of the disc 10. If the disc has more than one dark zone, other ratios are obtainable. Circuit 84 pulse output passes via an amplifier 88 and line 90 to a data record circuit 17 in which the direction of the continuous current over the data recording head DM (98) is reversed each time a pulse is received over line 90. Time information channel. For 14¢ minutes of each 15 minute period of meter M operation, the cam 26 allows contacts B of timer switch SW1 to be earthed, so that a steady current flows across time recording head TH (98) from right to left (Fig. 2) to record a negative polarity signal E on Fig. 3c. For the remaining 30 seconds, contacts A are earthed, reversing the current across the recording head to record a positive polarity signal F on Fig. 3c. The power sensing circuit 125 includes a timing capacitor 130 with a discharge resistor 122, and a latch circuit 124 formed by NAND gates 126, 128. A capacitor 137 provides D.C. power to the latch circuit 124 for at least 40 seconds following loss of power in line 49. The capacitor 130 becomes fully discharged in 20 seconds from cessation of power. Thus a power interruption of less than 20 seconds does not affect the latch circuit 124 or the transistors 117, 118 in the time record circuit, though the recorder will cease operation while the power is off. If power is not restored within 20 seconds, the latch circuit 124 changes state so that when power is restored, transistors 117, 118 are turned off and no current flows across the time recording head TH. On Fig. 3c, as power is restored the negative polarity signal changes to zero, at K, and remains so until the next operation of timer switch SW1, which gives a step LM from zero to  positive polarity. This produces the distinctive playback signal, Fig. 3d, of two half-amplitude positive pulses in succession, indicating a power interruption.