GB2142149A - Monitoring apparatus using phase locked loop - Google Patents

Abstract

Monitor apparatus, for example for monitoring the speed of a conveyor belt, has a transducer for providing a train of pulses, say one each revolution of a rotary member in contact with the belt, a phase-lock loop (PLL) arrangement 10 for receiving the train and for producing an output the frequency of which is a multiple of the frequency of said train and processing means for processing said output to determine the speed. The PLL arrangement 10 has a phase comparator, a voltage-controlled oscillator (VCO) 20 and a frequency divider 22 in a feed-back loop between the output of the VCO and an input of the phase comparator. An arbitrary number of pulses from the VCO is selected to be equal to a given distance of belt travel. Consequently, the frequency divider can be adjusted according to the diameter of the rotary member. <IMAGE>

Description

SPECIFICATION Monitor apparatus This invention relates to monitor apparatus.

Monitor apparatus according to the invention comprises a transducer for producing a train of pulses in response to a parameter being monitored, a phase-lock loop arrangement for receiving said train of pulses and for producing an output the frequency of which is a multiple of the frequency of said train of pulses and processor means for processing said output to determine the parameter, the phase-lock loop arrangement comprising a phase comparator, a voltage-controller oscillator and a frequency divider, the comparator having a first input connected to the transducer, an output connected to an input of the oscillator and a second input connected to a feed-back loop from an output of the oscillator, the loop containing the divider and the output of the oscillator being connected to the processor means.

A conveyor belt monitor apparatus will now be described to illustrate the invention by way of example only with reference to the accompanying drawings, in which: Figure 1 is a block diagram of the apparatus; and Figure 2 is a block diagram of the phase-lock loop arrangement shown in Figure 1.

The apparatus has a transducer (not shown), a phase-lock loop (PLL) arrangement 10 and a processor means comprising the several components for processing the output of the PLL arrangement 10.

The transducer may be, for example, an electro magnetic inductive device responsive to a hole in a disc forming part of a rotary member such as a roller or drum (not shown) in contact with a conveyor belt whereby one pulse per revolution of the rotary member is produced by the transducer.

The pulses from the transducer are fed to an input 14 for a signal conditioner 16. The conditioner 16 produces a square of quasi-square pulse in response to each input pulse and ensures that any spikes on the input pulse are not passed through to the PLL arrangement 10.

The PLL arrangement 10 (see particularly Figure 2) has a phase comparator 18, a voltage-controlled oscillator 20 and a frequency divider 22. A first input of the comparator 18 is connected to the conditioner 16. The output of the comparator 18 is connected, via a low-pass filter 28, to the input of the oscillator 20.

The output drive of the oscillator 20 is connected to the processing means via an output drive 32 and, in a feed-back loop containing the divider 22, to a second input of the comparator 18. The divider 22 is selectively adjustable by a 'set diameter' control 36.

The processor means is used to give a local read-out of belt speed and remote read-outs of belt speed and belt travel.

For determining belt speed, the processor means includes a 3-decade binary-coded decimal counter 38 which is connected to the output drive 32 of the oscillator 20.

The counter 38 is resetable by a reset pulse from a reference oscillator 40 which is connected to the counter 38 by selectively adjustable frequency dividers 42 and 44.

A remote indication of speed is obtainable from the counter 38. A first output from the counter 38 is connected to a digital-to-analogue converter 46, the converter 46 receiving the stored count from the counter 38 when the counter 38 is reset. The converter 46 is connected to a constant current output drive 48 which includes a ramp generator.

The output limits of the ramp generator, i.e. 0.4 volts (X) and 2.0 volts (Y), can be set to the limits of the range of belt speed which it is required to monitor.

The typical belt speed range is 30 to 999 feet per minute (0.15 to 4.57 metres per second) and consequently, the X and Y limits could be set to zero and to 1000 feet per minute, respectively.

The counter 38 can also be used to convert the stored count, upon reset, into a speed reading which is displayed on a locally mounted LED or LCD display 50.

The first output of the counter 38 is also connected, via latches (not shown), to magnitude comparators 52 and 54 which compare the count received from the counter 38 with pre-set high and low speed settings, respectively. The high and low speed settings in the comparators 52 and 54 are set by controls 56 and 58, respectively. If the count from the counter 38 is indicative of belt overspeed or belt slip, a signal is passed via an OR gate 60 to a timer 62 and then, after a delay period selected to prevent spurious tripping, via a NAND gate 64 to relay 66 which is operable to de-energise the conveyor belt motor drive.

A timer 48 is connected to the other input of the NAND gate 64 to prevent operation of the relay 66 to de-energise the drive during start-up of the conveyor.

The output drive 32 of the oscillator 20 of the PLL arrangement 10 is connected also to a frequency divider 70, the output from which is connected to a digital-to-analogue converter 72. The converter 72 is connected to a constant current drive 74 which includes a ramp generator. The divider resets every 251 pulses (at 48 pulses/6.284 feet - see below, 251 pulses is equivalent to 10 metres of belt travel). The X (0.4 volts) and Y (2.0 volts) limits of the ramp generator are set to zero and 251, repectively, so that at the remote location, a repeating ramp signal is received which is indicative of each 1 0m of belt travel. Such a signal can be used to determine the quantity of material conveyed by the conveyor belt, for example.

When the belt is travelling at a constant speed or the speed of the belt is changing slowly, the PLL arrangement is in lock, i.e. the frequencies of the inputs of the comparator 18 are in phase, and the output pulses from the voltage-controlled oscillator 20 are an accurate measure of the distance moved by the belt. Even during relatively rapid acceleration of the belt, e.g. on start-up, the PLL arrangement 10 tries to anticipate the arrival of the next pulse from the signal conditioner 16 by setting the oscillator 20 to give approximately the correct frequency, the accuracy of the frequency setting being improved after each pulse until the arrangement 10 can achieve lock.

An arbitrary number of pulses from the oscillator 20 of the PLL arrangement 10 is selected to be equivalent to a given distance of belt travel. Consequently, the control 36 can be used to set the frequency divider 22 such that the number of output pulses from the oscillator 20 (for each input pulse from the transducer) is equivalent to a distance of travel equal to the circumstances of the rotary member in contact with the belt, i.e. it is proportional to the diameter of the rotary member (typically in a range from 1" [0.025m] for a belt roller up to 48" [1.22m] for a belt drum). Thus, the apparatus can be readily set up according to the application to which it is applied.

In the embodiment described above, the arbitrary figure selected was 48 pulses for a distance of travel of 6.284 feet (1.92m).

Assuming a maximum belt speed of 1000 feet per minute, 1000 is divisible by 6.284 approximately 160 times and, consequently, for a travel of 1000 feet, the oscillator 20 will generate 7680 pulses or 128 pulses per second. Thus, to fully utilise the capacity of the counter 38, the counting period of the counter 38 is 999 divided by 128 which equals 7.81 seconds giving a reset frequency of 0.128Hz.

The reference oscillator 40 can be of a commonly available type which operates at a frequency of 32.768kHz and simply by setting the dividers 42 and 44 to divide that frequency by 256 and 1000, respectively, the reset frequency of 0.128Hz is obtained.

Clearly, other values of the multiples and other gate periods can be selected to suit the accuracy required or the application.

Instead of inductive pick-up at the transducer, optical, mechanical or other modes may be used.

The transducer could respond to marks, apertures etc. carried by the belt instead of the drum.

The invention is applicable to monitoring of movement outside the field of conveyor belts, for example vehicle speed and travel monitoring, position monitoring, cable travel.

Claims (10)

1. Monitor apparatus comprising a transducer for producing a train of pulses in response to a parameter being monitored, a phase-lock loop arrangement for receiving said train of pulses and for producing an output the frequency of which is a multiple of the frequency of said train of pulses and processor means for processing said output to determine the parameter, the phase-lock loop arrangement comprising a phase comparator, a voltage-controlled oscillator and a frequency divider, the comparator having a first input connected to the transducer, an output connected to an input of the oscillator and a second input connected to a feedback loop from an output of the oscillator, the loop containing the divider and the output of the oscillator being connected to the processor means.

2. Apparatus according to claim 1, in which a signal conditioner is interposed between the transducer and the phase comparators whereby the phase comparator receives square or quasi-square pulses free from transitory excursions.

3. Apparatus according to claim 1 or claim 2, in which the processor means comprises a binarycoded decimal counter connected to the oscillator for receiving the output therefrom.

4. Apparatus according to claim 3, in which said multiple and the reset frequency of the counter are selected such that, when the frequency of said train of pulses is at a maximum, the number of pulses received by the counter in each counting period is substantially equal to the capacity of the counter.

5. Apparatus according to claim 3 or claim 4, in which the counter includes circuit means for converting the number of pulses counted in each counting period into a speed of movement signal which is fed to a display unit.

6. Apparatus according to any one of claims 3 to 5, in which the processor means further comprises a digital-to-analogue converter the output from which is connected to a constant current output drive including a ramp generator for providing a signal to a location remote from the apparatus, the input of the converter being cennected to the counterwhereby the converter receives the number of pulses counted in each counting period and the ramp generator generates the signal which is proportional to the number of pulses received by the converter and is representative of speed of movement.

7. Apparatus according to any one of claims 3 to 6, in which the processor means further comprises at least one magnitude comparator having an input connected to the counter and an output connected to trip means whereby, if the number of pulses received by the magnitude comparator is outside a limit set in the magnitude comparator, the trip means is operated.

8. Apparatus according to any preceding claim, in which the processor means further comprises in a series connection a frequency divider a digital-toanalogue converter and a constant current output drive including a ramp generator for providing a signal to a location remote from the apparatus, the divider being connected to the oscillator and being arranged to reset after a predetermined number of pulses have been counted, said predetermined number being proportional to an extent of travel whereby the signal generated by the ramp generator is representative of said extent of travel.

9. Apparatus according to any preceding claim, in which the frequency divider of the phase-lock loop arrangement is adjustable whereby the multiple is selected according to a dimension of equipment from which the transducer derives said train of pulses.

10. Apparatus according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.