Patent GB-858647-A (GB)
Title: Data scanner monitoring alarm system
IPC: G08B26/00
Filed: 1959-05-13
Abstract: 858,647. Electric alarm systems. FOXBORO CO. May 13, 1959 [May 21, 1958], No. 16454/59. Class 118 (1). Relates to a visual and audible alarm system for monitoring a group of variable conditions on the basis of scanning representatives of the conditions, having a plurality of visible alarms and one audible alarm in which are provided means for locking up the alarm units on receipt of an off normal signal, means for resetting the visual alarm in receipt of a normal signal and manual means for resetting the audible alarm. As described, the outputs from a number of thermo-couples used for temperature monitoring are sequentially connected by means of a programmer 11 through an ambient temperature compensating circuit 22 to two parallel paths in which the outputs are amplified by amplifiers 23, 24 and then compared with high and low reference potentials from decade dividers 35, 37, respectively, whose values correspond to the permissible temperature limits of the selected thermo couples. The appropriate reference potentials are selected by means of pin boards 36, 38. The two signals resulting from these comparisons are fed via amplifiers 27, 29 into discriminators 28, 30 and if the temperature is either too high or too low the discriminator outputs operate relays in an alarm circuit which lights an appropriate indicator lamp 80 showing where the off normal condition has occurred and also sounds an audible alarm 32. The audible alarm may be cancelled manually by button 83 to leave the visible indication only and if the next time the thermo couple is scanned the signal has reverted to normal, the visible indication is cancelled automatically. Programmer.-The programmer comprises a pulser 14 and a flip-flop 15 which acts as a divide by two circuit to operate relays 17. A first pulse opens the contact 74 in the alarm and produces an output from the flip-flop 15 which closes switches 10, 62, 77, and a second pulse closes the contact 74 connecting the discriminator output to the alarm. A third pulse opens contact 74 again and closes the switches associated with the next thermo couple, and the cycle thus repeats. Dividers and pin boards.-The decade divider 37 for the low reference potential comprises three resistance elements 42, 43 and 44 powered from a battery 45. One of the three portions of the element 42 may be selected by means of the " tens " coils in the pin board 38 energization of which causes the contacts 46 to be connected between contacts 52 and 53, 48 and 49, or 50 and 51. As shown, the reference line corresponding to the first thermo-couple has a pin 56 inserted in the line to the second " tens " coil 65 so that when switch 65 closes simultaneously with the connection of the first thermo-couple by the switch 10, the + 48-volt point is connected through the pin 56 on to the coil 65 to cause the switch contacts 46 to be connected to contacts 48, 49. Similar tapping points are provided on the elements 43, 44 associated with each of the coils in the " units " and " tenths " sections of the pin board so that any desired output may be obtained across resistor 41. A similar pin board 36 and decade 35 are provided for the high reference potential to give an output across resistor 40. Diodes, e.g. 62<SP>1</SP> are included in the horizontal leads in the pin boards to prevent undesirable interaction between the banks of the board. Comparison units.-The signal fed into the amplifier 29 consists of the differences between the thermo-couple signal from amplifier 24 and the lower reference potential and is positive for normal conditions. Similarly, that fed into the amplifier 27 is the difference between the thermo-couple signal from amplifier 23 and the high reference potential and is negative for normal conditions. Connected to the outputs of the discriminators are relays 70, 71 each having a set of changeover contacts 72, 73 respectively, which are movable to either a normal position N or to off-normal positions HI for 72 and LO for 73 depending on the polarity of the signal. Alarm unit.-Associated with each thermocouple are a switch 77, a coil RIM operating contacts 79, 81, 82, resistor 78 and a lamp 80. On receipt of an off-normal condition coil RCM is energized closing contact 86 to energize coil RCL3. This holds in over contact 84, opens contact 88 and closes contact 87 to give an audible alarm, which can be cancelled by button 83. Relay RLM is energized via contacts 77, closing self-hold contacts 79, lamp circuit contacts 81 and also a further contact 82 from which an output may be taken. If the offnormal condition persists at the next measurement on the thermo-couple, the lamp remains lit, but the resistor 78 effectively in parallel with coil RCL3 limits the current through the coil to prevent an audible alarm being regiven. On receipt of a normal signal from the thermocouple, coil RLR is energized closing contacts 89 and shorting out coil RLM via contacts 77, 88 and 89, thus if RLM had been previously energized, giving a visual alarm, the normal signal would cancel this alarm. Fig. 4 (not shown) is a system using a modified alarm unit, the overall working of the system being generally the same as that described above.