Patent ES-339561-A1 (ES)
Title: Automatic weighing scale calibration
IPC: G01G19/04
Filed: 1967-04-20
Abstract: In apparatus for weighing railway wagons 2 a transducer converts the weight of an axle to an amplitude signal which is in turn converted to digital form, means are provided for detecting and storing the digital magnitude of the drift of the circuit and means for connecting subsequent measuring operations to compensate for the drift. The weigh rail 6 is supported on four load cells 10 connected in a bridge so as to produce across leads 12 a voltage equivalent to the load. This voltage passes through a filter 14 and potentiometer 18 to a voltage-controlled oscillator 20 producing a proportional frequency on lead 22. These pulses are gated at 24 for a set interval, through a circuit 48 which subtracts 100 pulses, to a counter 46 indicating the weight to a recorder 58. The operation of the circuit is initiated by wagon-position sensers 30 operating a trigger 32 to reset and start a timer counter 36. This counts pulses from a standard frequency oscillator 38 oscillating at 100,000 cycles/second. The counter is set to count 50,000 pulses (i.e. 0-5 second) and give a pulse on lead 40 to open gate 24. After a further 0.2 second the counter closes the gate. For the initial calibration of the system there is applied a standard weight of 40,000 pounds, which is about the value of most expected weighings. Then switch 128 is closed to reset and start counter 36. At a count of 40,000 (0.4 second) it energizes lead 132 to open gates 102, 104. 0À1 of a second later it energizes lead 134 to close gate 102. Gate 102 has therefore passed 10,000 pulses to storage register 110 and via gate 104 to weight counter 46. Register 110 is a counter which counts up to 200 and starts again, each cycle passing one pulse to counter 112 and another pulse on lead 140 to close gate 104 so that counter 46 receives 200 pulses. 0.5 of a second after the start counter 36 opens gate 24 for 0.2 of a second. During this time pulses from oscillator 20 pass to the counter, the first 100 being subtracted by the counter 48. The frequency derived from the standard load of 40,000 lb. is to be set so that each pulse represents ten pounds. As there is already a count of 200 in the counter 46 and a hundred subtracted, the value in the counter at the end of the 0.2 second should be 4100. The potentiometer 18 is adjusted and the test repeated until a count of 4100 is achieved. Switch 123 is operated to close relay 122 connecting a variable resistor 118 in place of resistor 116 and resistor 118 is manually adjusted to give a reading of 4200, which because of the pre-loading of 200 and the subtraction of 100 means that 4100 presses have been produced. To check the calibration drift in normal use the operator presses switch 125 to actuate relay 124 which holds for at least 0À7 of a second. Contact a connects the calibrating resistor 118 in circuit. Contact b starts a time counter 361 and contact c resets counters 110, 112. Counter 361 counts pulses from oscillator 38 and, after 0.5 of a second, opens gate 106 for 0.2 of a second. During that time 4100 pulses should pass to the register 110, causing it to cycle 20 times and retain a count of 100. Counter 112 should have received 20 pulses, counting from 0 to 19 and reverting to 0. Flip-flop 160 is set at all counts except-zero, and reset at zero. When set it provides a danger signal on lead 161, indicating that an excessive correction has been made. If the system has remained in correct calibration therefore, the result of the check operation is to place a count of 100 in register 110 and a count of zero in counter 112. In subsequent weighing operations this value of 100 is entered from register 110 to counter 142 as follows. When the sensors 30 indicate that a wagon is in position on the weigh rail, a pulse on line 34 starts counter 36. After 0.4 of a second it opens gates 102, 104 and then, after a further 0À1 of a second, it closes gate 102 only. The 10,000 pulses during this period go into register 110 which starts from a count of 100. At the same time pulses from gate 102 go through the gate 104 to counter 46. After 100 pulses the register 110 changes from 199 to zero and sends a pulse to close gate 104 so that only 100 pulses go to the counter 46. Register 110 cycles 50 times finishing up with a count of 100. In each subsequent measuring cycle this count of 100 in counter 46 corresponds to the 100 subtracted by the counter 48 so that the final count is a correct representation of the weight. The counter accumulates the weights of the four axles of a wagon under the control of counter circuit 52. If the system is out of calibration, the initial check operation causes the resistance 118 to enter a value different from 4100 by the error e. The value in register will therefore be 100 + e, if e is an excess. This number is initially transferred to counter 46. During the weighing cycles which follow the number of pulses fed to counter 46 will also be in excess of the correct figure by approximately e and this value is subtracted by the initial loading of the counter to 100 + e. Specifications 1,165,221 and 1,108,982 are referred to.