GB1578320A

GB1578320A - Fan monitoring arrangement

Info

Publication number: GB1578320A
Application number: GB632476A
Authority: GB
Original assignee: TROLEX PROD Ltd
Current assignee: TROLEX PROD Ltd
Priority date: 1977-02-28
Filing date: 1977-02-28
Publication date: 1980-11-05

Description

(54) A FAN MONITORING ARRANGEMENT (71) We, TROLEX PRODUCTS LIMITED, a British Company, of Newby Road, Hazel Grove, Stockport SK7 5DY, Cheshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to a vibration monitoring apparatus.

All forms of apparatus comprising one or more moving parts produce vibrations giving an indication of the operational state of the apparatus. In many situations it is advantageous for a close check to be kept on the operational state of apparatus; in others it is absolutely essential that such a check be kept. Thus, for example, in an underground coal mine ventilation is an ever present problem. In a relatively small mine, it may be possible to provide the necessary air circulation simply by providing a ventilation fan on the surface at the head of the mine upcast shaft. This fan sucks air out of the mine from the coalface via an upcast shaft and a return roadway and this air is replaced by air flowing down the downcast shaft and along a roadway to the coalface.In a larger mine the increased resistance to airflow caused by the longer runs and deeper shafts means that a more powerful fan must be provided at the surface. A position is reached where the additional fan power which must be provided for a marginal increase in air circulation is prohibitively large. To maintain the air circulation when this occurs, booster fans and auxiliary fans are provided at chosen intervals along the roadways underground. The decision to place such equipment in the mine itself, where the ever present methane could form an explosive mixture with air, is a difficult one as a malfunction in the fan may cause ignition of the mixture with tragic consequences. This danger could be either reduced or virtually eliminated if the performance of the fans could be monitored so as to provide an early indication of possible abnormal operation.

According to the present invention there is provided a vibration monitoring apparatus comprising a transducer for converting the mechanical vibrations of a vibration producing device into electrical signals, means for selecting from the frequency spectrum of the signals produced, bands of signals, the various amplitudes of the signals in these bands appertaining to the health or conditoin of different components of the vibration producing device, level detector means for detecting the level of the various signal bands selected by the means for selecting and means of indicating the various signal levels, sail level detector means comprising means for discriminating between different signal levels.

A preferred embodiment of the invention may include any one or more of the following preferred features: - (a) The means for selecting bands of signals comprises a filter used in conjunction with a selective amplifier.

(b) The level indicator means comprises a meter.

(c) The means of indicating comprises a plurality of lamps operative to react to signals at the different signal levels.

(d) Means are provided for tuning the apparatus so that a normal signal level corresponds to a standard fixed level on the meter of (b).

(e) The signal from the transducer is split and means for selecting detector means and indicator means are provided for different parts of the frequency spectrum of the signal produced by the transducer.

In order that the invention may be more clearly understood, one embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which : - Figure 1 shows a block circuit diagram of a vibration monitoring system.

Figure 2 is a graph of the variation of amplitude with frequency for the frequency range of the signal to be monitored, Figure 3 indicates the various conditions of the system to be monitored, and Figure 4 shows a particular type of fault condition.

Figures 4a and 4b show a full circuit diagram of a part of the monitoring system shown in block form in Figure 1, Figures 5a and Sb show a full circuit diagram of another part of the monitoring system shown in block form in Figure 1, and Figure 6 shows an external view of a cabinet for housing equipment of the sort shown in block form in Figure 1.

Referring to the drawings, a piezo-electric transducer 1 is fitted to the body of the machine whose vibration is to be montiored. The position of the transducer 1 is carefully chosen so that it picks up all the vibrations produced by the machine. It comprises two piezo-electric crystals fixed together back-to-back and supplied from a 10 volt supply. These crystals are connected to an internal charge amplifier and then to a wide band amplifier 2 and the transducer 1 and charge amplifier are housed iP the same housing. In the case of a coal mine application it is important that this housing should be of aluminium.

The output from the amplifier 2 is fed to a low pass filter 3, a high pass filter 4 and a monitoring terminal 5. The monitoring terminal enables the complete range of the vibrations received by the transducer 1 to be monitored, or recorded by some external means. The low pass filter 3 works in conjunction with a low frequency amplifier 6 to pass only a low frequency section of the total frequency spectrum picked up by the transducer 1 and amplified by the amplifier 2. In this particular embodiment, where the machine is a fan for a coal mine application, the low pass filter allows through only frequencies below 60 Hz and the low frequency amplifier has a low frequency cut off point of 8 Hz. The filter 3 and amplifier 6 together therefore pass signals having frequencies in the band width 8 Hz to 60 Hz.

A similar arrangement obtains in the high frequency section of the circuit where the high pass filter 4 works in conjunction with a high pass amplifier 7 to pass only a high frequency section of the total frequency spectrum. In this embodiment, the high pass filter passes frequencies over 200 Hz and the high frequency amplifier cuts off at 10 Hz thus given a high frequency band width of 200 Hz to 10 KHz.

The setting devices are respectively provided between the low pass filter 3 and the low frequency amplifier 6 and between the high pass filter 4 and high frequency amplifier 7. The purpose and operation of these devices 8 and 9 will be described later.

The outputs from the low and high frequency amplifiers leads to respective detectors 10 and 11 and to respective low and high frequency monitoring terminals 12 and 13. The output from each detector 10, 11 leads to three condition indicator lights 209-211 for detector 10 and H1, H2 and H3 for detector 11.

Figures 4a and 4b show in detail the low frequency channel of the complete monitoring circuit shown in Figure 1. The output signal from the signal conditioning amplifier 2, which is a standard amplifier with frequency compensation, is fed into the low frequency channel at terminal 20.

The low pass filter 3 is constituted by the three resistors 3032 and the three capacitors 33-35. Setting device 8 is constituted by the variable resistor 25. The output from the filter 3 is then fed to the amplifier 6 comprising an integrated circuit amplifier 60 and associated resistors and capacitors. Two further integrated circuit amplifiers 101 and 102 form the basis of the positive peak detecting circuit 10 having a fast updating and slow decay time.

A zener diode 201 provides, in conjunction with the four series connected resistors 202-205, reference levels for the level detectors circuits formed basically by the integrated circuits 206-208. Outputs from the three integrated circuits 206-208 are fed through intermediate circuitry to respective light emitting diodes 209-211.

The outputs of integrated circuits 207 and 208 are additionally "ANDed" together at transistor 212 and the "ANDed" signal appears at 213. The intermediate circuitry between the integrated circuit 206 and light emitting diode 209 comprises a further integrated circuit 214 which together with the circuit 206 and other intermediate components forms a self-programming timer. An output alarm signal appears at terminal 215 after a time proportional to the input signal applied to integrated circuit 206. Thus, with a small percentage increase in that input signal, there will be a long time delay, and vice-versa. Both of the light remitting diodes may be connected to earth through a normally open switch 216, whereas the diode 211 is permanently earthed. The diode 211, when lit, indicates a system fault condition, diode 210, a first order (or non-critical) fault condition and diode 209, when lit, a second order fault condition for which urgent action is required. The high frequency arm of the monitoring circuit is very similar to the low frequency arm just de scribed, the main difference being in the provision of a high pass filter instead of a low pass filter at the input end of the circuit.

The operation of the system will now be described. The amplitude-frequency distribution curve for the fan whose operating condition is to be monitored is shown in Figure 2 for various operating conditions of the fan. The curve for the normal operating condition is shown in full line, that for an abnormal operating condition due to an out of balance fan in dotted line and that for an abnormal operating condition due to faulty bearing in dash-dotted line. It will be seen that for a normally operating fan supplied from a 50 Hz frequency mains supply, two quite pronounced peaks in the curve are produced at 25 Hz and 50 Hz and the amplitude of the vibrations tends to increase fairly linearly with frequency after 200 Hz.

In an out of balance fault condition the two 25 Hz and 50 Hz peaks increase in ampltiude as shown in dotted line. The magnitude of the increase determines the seriousness of the fault condition and thus the degree of urgency of any corrective action. The duration of the fault condition is also of importance for the system must be able to distinguish between a fault condition and an externally influenced transient condition caused, for example.

by an accidental collision of a piece of equipment with a fan casing. An indicated fault condition in a situation such as this could bring the system into disrepute with possible dangerous consequences in the event of a real fault condition arising.

A working fan is important to a safe working environment in a coal mine and it is therefore equally important that the fan should not be needlessly shut down. The requirement for urgent action such as shut down is therefore a combination of the magnitude of fault condition and the duration of that condition. In addition to an "urgent action required" condition two other conditions are indiacted, a first where a fault condition is present but is not of critical magnitude and a second where, under normal fan operation, the signal magnitudes detected are less than they should be signifying a fault in the system itself caused, for example, by a displaced transducer.

All three conditions are indicated in Figure 3 and 4 for an out of balance of the fan type of fault. In each of these figures, the percentage fault is shown plotted against time. The normal condition is indicated by the 100% line, an "urgent" fault condition from 200% upwards, a fault condition from 150% upwards, and a system fault condition from 50% downwards. Since the level of signal produced by different fans under normal operating conditions varies, it is necessary to set up the system by tuning it to the fan. This is achieved by variable controls 8 and 9 which are adjusted until a fixed standard level is obtained on meters connected to monitoring terminals 14 and 15 of respective detectors 10 and 11. Should the amount of adjustment not be sufficient to obtain zero level then the degree of amplification given by the amplifier 2 may also be altered.

The non-urgent fault and system fault levels are simple magnitudes determined empirally. If the signal level falls below 50% of normal then 211 lights; if the signal level rises 50% above normal then 210 lights. If the signal level rises above 100% above normal then whether 209 lights will depend upon the duration of the high level of signal. At with the other fault signal levels, the urgent fault signal levels are chosen empirally. In this case if a 400% fault signal level persists for over 2 seconds or a 200% fault signal level for over 20 seconds 209 will light. These two points are joined on the graph of Figure 4 and intermediate fault signal levels intermediate these points and located to the right of the joining line will light 209.

The method used for a faulty bearing condition is similar to the out of balance condition just described, but the empirical figures chosen are different and are determined by integration from the high frequency part of the curve of Figure 2 between 200 Hz and 10KHz. Furthermore, the meters are calibrated to read the peak signal within that frequency range.

The alarm signal may be used to operate alarm circuitry. The alarm circuitry is shown on Figure 5A and 5B for a bank of three fans. Each fan has a monitoring circuit of the type just described and thus the alarm circuitry must be capable of receiving alarm signals on any one of twelve output terminals. The circuit shown in Figure 5A thus has twelve inputs in two banks Fl and F2 of three and one bank S of six. Bank Fl receives alarm signals for a serious out of balance condition bank F2 receives alarm signals for a serious bearing condition and bank S alarm signals for a system fault condition which as described earlier is joined with non-critical balance or bearing fault conditions.Thus, specifically terminal 215 is connected to the third terminal of the bank Fl, and the other two terminals of that bank are connected to corresponding terminals of the other fan monitoring circuits; and terminal 213 is connected to the six terminal of bank S. The fifth terminal of the bank S will be connected to the corresponding high frequency system fault terminal of the same monitoring circuit, while the other four terminals will be connected to corresponding terminals of the monitoring circuits of the other two fans. The banks Fl and F2 control through respective transistors 50 and 51 the relay contacts of two tripping relays (not shown), so that in the event of an alarm signal in either of the banks all three fans will automatically shut down.

Bank S also controls, through a time delay circuit, a warning relay (not shown).

It is advantageous, after shut down, to have some indication of which fan and what type of fault (balance or bearing) caused shut down. This may be provided by small magnetised discs which flip into a certain position under the action of a magnetic field influenced by the alarm signal current. They remain in this position until reset. The operative sides of the discs may be brightly coloured to aid recognition.

The monitoring and fault indication equipment are advantageously housed in a cabinet with the light emitting diodes in the same physical relationship as the fans themselves. An example is shown in Figure 6 for four fans arranged in two parallel rows each of two fans in series.

Each fan has three rectangles each containing a light emitting diode. The three rectangles respectively represent a serious balance, serious bearing and other fault conditions. The monitoring meters mentioned earlier are shown to the right of the console display. The whole display is fed from a flame proof power supply.

For mining applications, it is necessary that the circuitry should be intrinsically safe in order to avoid sparking. Capacitors having charges which could cause a spark if discharged by an accidental short circuit are therefor connected in series with resistors of suitable value. Several examples of these can be seen in the amplifier section 6 of the circuit of Figure 4a.

The above described apparatus thus provides a discriminating method of accurately detecting the existence of the two fault conditions which are non-urgent.

chine in continuous operation. The electronic nature of the apparatus enables the condition of the machine to be monitored from a remote location and this is of particular importance in mining locations. In addition sufficient versatility is built into the apparatus to enable fault conditions which are urgent to be distinguished from fault condtiions which are non-urgent.

This again is of particular significance in mining applications where it is important that the fan should not be shut down unless it is absolutely necessary. The apparatus above is of course for installation.

Small portable units operating on the same principles but without the alarm circuitry may also be produced. I1rcse would be battery driven and would be taken from installation to installation to monitor each installation in turn.

WHAT WE CLAIM IS: - 1. A vibration monitoring apparatus comprising a transducer for converting the mechanical vibrations of a vibration producing device into electrical signals, means for selecting from the frequency spectrum of the signals produced, bands of signals, the various amplitudes of the signals in these bands appertaining to the health or condition of different components of the vibration producing device, level detector means for detecting the level of the various signal bands selected by the means for selecting and means of indicating the various signal levels, said level detector means comprising means for discriminating between different signal levels.

2. A vibration monitoring apparatus as claimed in Claim 1, wherein the means for selecting comprises a filter used in conjunction with a selective amplifier.

3. A vibration monitoring apparatus as claimed in Claim 1 or 2, wherein the level indicator means comprises a meter.

4. A vibration monitoring apparatus as claimed in Claim 1, 2 or 3, wherein the means for indicating signal level comprises a plurality of lamps operative to react to signals at the different signal levels.

5. A vibration monitoring apparatus as claimed in any preceding claim, wherein means are provided for tuning so that a normal signal level corresponds to a given level on the means for indicating.

6. A vibration monitoring apparatus as claimed in any preceding claim, wherein means are provided for splitting the signal from the transducer.

7. A vibration monitoring apparatus as claimed in Claim 6, wherein means for selecting detector means and indicator means are provided for different parts of the frequency spectrum of the signal produced by the transducer.

8. A vibration monitoring apparatus as claimed in any preceding claim, wherein the transducer comprises a piezo-electric crystal.

9. A vibration monitoring apparatus as claimed in Claim 8 wherein the transducer comprises two piezo-electric crystals fixed back to back and connected to an internal charge amplifier and then to a wide band amplifier.

10. A vibration monitoring apparatus as claimed in Claim 9, wherein the output from the wide band amplifier is connected

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the corresponding high frequency system fault terminal of the same monitoring circuit, while the other four terminals will be connected to corresponding terminals of the monitoring circuits of the other two fans. The banks Fl and F2 control through respective transistors 50 and 51 the relay contacts of two tripping relays (not shown), so that in the event of an alarm signal in either of the banks all three fans will automatically shut down. Bank S also controls, through a time delay circuit, a warning relay (not shown). It is advantageous, after shut down, to have some indication of which fan and what type of fault (balance or bearing) caused shut down. This may be provided by small magnetised discs which flip into a certain position under the action of a magnetic field influenced by the alarm signal current. They remain in this position until reset. The operative sides of the discs may be brightly coloured to aid recognition. The monitoring and fault indication equipment are advantageously housed in a cabinet with the light emitting diodes in the same physical relationship as the fans themselves. An example is shown in Figure 6 for four fans arranged in two parallel rows each of two fans in series. Each fan has three rectangles each containing a light emitting diode. The three rectangles respectively represent a serious balance, serious bearing and other fault conditions. The monitoring meters mentioned earlier are shown to the right of the console display. The whole display is fed from a flame proof power supply. For mining applications, it is necessary that the circuitry should be intrinsically safe in order to avoid sparking. Capacitors having charges which could cause a spark if discharged by an accidental short circuit are therefor connected in series with resistors of suitable value. Several examples of these can be seen in the amplifier section 6 of the circuit of Figure 4a. The above described apparatus thus provides a discriminating method of accurately detecting the existence of the two fault conditions which are non-urgent. chine in continuous operation. The electronic nature of the apparatus enables the condition of the machine to be monitored from a remote location and this is of particular importance in mining locations. In addition sufficient versatility is built into the apparatus to enable fault conditions which are urgent to be distinguished from fault condtiions which are non-urgent. This again is of particular significance in mining applications where it is important that the fan should not be shut down unless it is absolutely necessary. The apparatus above is of course for installation. Small portable units operating on the same principles but without the alarm circuitry may also be produced. I1rcse would be battery driven and would be taken from installation to installation to monitor each installation in turn. WHAT WE CLAIM IS: -

1. A vibration monitoring apparatus comprising a transducer for converting the mechanical vibrations of a vibration producing device into electrical signals, means for selecting from the frequency spectrum of the signals produced, bands of signals, the various amplitudes of the signals in these bands appertaining to the health or condition of different components of the vibration producing device, level detector means for detecting the level of the various signal bands selected by the means for selecting and means of indicating the various signal levels, said level detector means comprising means for discriminating between different signal levels.

through series connected high and low pass filters forming part of the means for selecting to a monitoring terminal.

11. A vibration monitoring apparatus as claimed in Claim 10, wherein means for selecting also comprises a low frequency amplifier provided for operation in conjunction with the low pass filter to pass only a low frequency section of the total frequency spectrum picked up by the transducer.

12. A vibration monitoring apparatus as claimed in Claim 10 or 11, wherein the means for selecting also comprises a high frequency amplifier provided for operation in conjunction with the high pass filter to pass only a high frequency section of the total frequency spectrum picked up by the transducer.

13. A vibration monitoring apparatus as claimed in Claim 12, when appendant to Claim 11, wherein two setting devices are respectively provided between the low pass filter and low frequency amplifier and between the high pass filter and high frequency amplifier to enable the device to be tuned to the equipment to be monitored.

14. A vibration monitoring apparatus as claimed in any preceding claim, wherein the means for detecting the level of the signal selected comprises means for integrating the signal over a predetermined time.

15. A vibration monitoring apparatus as claimed in any preceding claim, wherein the means for giving an indication of the signal level comprises alarm circuitry.

16. A vibration monitoring apparatus substantially as hereinbefore described with reference to the accompanying drawings.

17. A fan comprising a vibration monitoring apparatus as claimed in any preceding claim.