DETECTOR DEVICE FOR OPERATIONAL MONITORING OF A MACHINE OR A PROCESS

Abstract: Detection apparatus for monitoring the operation of a machine or process for the purpose of determining whether the machine or process is in operation or not. The detection apparatus includes a vibration sensor (2), with a signal processing unit (3) and an output unit (5, 6, 8) connected thereto. The signal processing unit (3) has amplification and filtering means adapted for filtering the signal from the vibration sensor (2) to a frequency band containing a characteristic frequency for the normal operational state of the machine or process. Provided that the signal has a characteristic frequency and amplitude distribution corresponding to the normal operational state, a demodulation circuit converts this signal to a direct voltage signal, which is sent to the output unit (5, 6, 8) via a threshold value detection circuit, the output unit sending a positive operational status indication signal.

Description: DETECTOR DEVICE FOR OPERATIONAL MONITORING OF A MACHINE OR A PROCESS The invention relates to detection apparatus for monitoring the operation of a machine or a process for the purpose of determin¬ ing whether the machine or process is in operation or not. Apart from machines, conveying equipment and the like, it shall also be possible to use the detection apparatus for detecting liquids, gases or other materials when they are conveyed in pipe systems and the like. The invention has its primary field of use within industry, in waterworks, sewage plants and heating plants, where continuous control of the machines involved is necessary. The invention can also be applied to machines in ships and off-shore works, where there is a similar need of monitoring different machines and conveying equipment . Known apparatus with the same purpose as the present invention are usually based on optical or inductive detection or monitoring the feed voltage to a drive motor for driving the machine in question. This kind of apparatus has certain drawbacks. For example, optical detection requires cleaning as well as the control of the set distance between a scanning unit and a moving machine part. Inductive detection also requires similar distance control. These two principles have also the drawback that they comprise two separate units, namely a scanning unit and an amplifying unit, with the necessary cables therebetween. Monitoring the voltage of a drive motor further has the disadvantage that the feed voltage can be applied to the motor without the motor working, e.g. it is stationary due to a break in a motor winding, or it is rotating but mechanically disconnected from the machine it is to drive. In contradistinction from these known apparatus, the detection apparatus in accordance with the invention is based on electron¬ ic components and circuits, which are connected to a vibration sensor. More specifically, the detection apparatus is of the kind disclosed in the preamble to claim 1. Such apparatus is already known per se, although it is intended for such monitor¬ ing of the operation state dealing with the discovery of smaller variations coming from wear, or other faults which should be attended to. The object of the present invention is, on the contrary, solely to determine whether the machine or process in question is in operation or not, and it is desirable to achieve this object with as simple aids as possible while retaining high reliabili- ty. This object is achieved with a detection apparatus having the distinguishing features disclosed in the characterizing part of claim 1. The vibration sensor included in the detection apparatus thus receives and converts to an electrical voltage signal the oscil¬ lations generated in operation by the monitored machine or pro¬ cess apparatus. This signal is taken to a signal processing unit, which is adapted to recognize the characteristic signal, in terms of frequency and amplitude distribution, which the machine or apparatus causes in operation. The signal processing unit suitably includes electronic circuits for filtering, amplifying, intregration, delay, demodulation and threshold value detection, as is disclosed in the claims and described in more detail below with reference to the accompanying drawings, where Fig. 1 is a block diagram of the units included in the detection apparatus, and Fig. 2 is a block diagram of the partial circuits included in the signal processing unit of the apparatus. The detection apparatus 1 illustrated in Fig. 1 is mounted on a machine or other mechanical device for monitoring its operation¬ al state, and includes a vibration sensor 2, which converts oscillations generated during operation into an alternating voltage signal. A signal processing unit 3 (described in more detail hereinafter) receives this electrical signal. The signal processing unit 3 is calibrated in manufacture, or by setting with the aid of setting means 4, to the characteristic frequency and amplitude distribution generated by the mechanical device, and it sends a positive operational status indication signal to an output unit solely under the condition that the frequency and amplitude characteristic of the signal sent from the vibration sensor 2 agrees with the signal characteristic registered in the signal processing unit 3. The output unit includes an indication circuit 5, the function of which is to indicate detection and which is primarily used for setting the characteristic of the unit 3 with the aid of the setting means 4. In addition, the output unit includes a relay circuit 8, which has the task of adapting the operational status indication signal to a gal- vanically separated output signal, e.g. for transmitting to a remote control room. A voltage stabilization circuit 7 achieves a stable, internal voltage supply to the electronic circuits. A condition circuit 6 can be put in between the signal processing unit 3 and the relayed circuit 8 if some other function of the relay circuit is desired. The condition circuit 6 can comprise, for example, conventional circuit elements such as inverters, gates, counters etc. and consequently does not need to be described here in more detail. The vibration sensor 2 can be of a desired type, e.g. piezo-resistive, piezo-electric, electro- dynamic, electrostatic, electromagnetic or magnetostrictive. As will be seen from Fig. 2, the signal processing unit 3 has an amplifyer circuit 31 connected to its input, e.g. comprising one or more series-connected operational amplifiers. The gain factor can be set with the aid of an adjusting means 32, which con¬ stitutes a variable attenuator. The output of the amplifier circuit 31 is connected to a filter and amplifier circuit 33, preferably comprising active filters, alternatively digital filters of bandpass, lowpass and/or highpass type. These filters are connected in series and/or in parallel to obtain the fre¬ quency and amplitude characteristic sought for. In certain cases the frequency characteristic of the filter and amplifier circuit 33 may need to be adjusted after installation for better adap- tion to the desired task. This can be achieved by further ad¬ justing means 34, which comprise one or more variable resistors. In this adjustment the limiting frequency or center frequency of the participating filters is changed. The output of the filter and amplifier circuit 33 is connected to a demodulation circuit 35 which, provided that the signal has the characteristic frequency and amplitude distribution, converts the incoming alternating voltage signal to an outgoing direct voltage. Time delay circuits 36 and 39 are connected here, which have the task of reducing the rapidity of the signal processing units and thus increasing detection reliability. It is suggested that the time delays should attain to 1-10 s. In their simplest form, the delay circuits 36 and 39 may comprise a resistor, or if so desired, they can be made variable and be adjusted by further adjusting means 37 and 40. The output of the demodulation circuit 35 is connected via the delay circuit 36 to an integra¬ tion circuit 38. The direct voltage applied here can be convert¬ ed in the integrator 38 to an envelope signal. In its most simple form the integrator may comprise a capacitor. The posi¬ tive direct voltage envelope from the integrator 38 is applied to a threshold value detection circuit 41 via the delay circuit 39. The threshold value detection circuit 41 is adapted such that when the incoming direct voltage envelope attains or ex¬ ceeds a threshold voltage, preset in the threshold value detec¬ tion circuit, a positive indication signal is sent on the out- put, which denotes that operation is in progress. The threshold value detection circuit 41 may comprise a comparator-connected operational amplifier.

Claims: C L A I M S 1. Detection apparatus for monitoring the operation of a machine or a process for the purpose of determining whether the machine or process is in operation or not, including: a vibration sensor (2) operatively connected to the machine or process, said sensor sending an electrical signal in re¬ sponse to the operational state of the machine or process, a signal processing unit (3) connected to the vibration sensor (2) for amplifying and filtering said electrical signal, and an output unit (5,6,8) connected to the signal processing unit (3) for sending an operation status indication signal, c h a r a c t e r i z e d i n that - the amplifying and filtering means (32,33) of the signal processing unit are adapted to filter said signal to a frequency band containing a characteristic frequency for the normal operational state of the machine or process, the signal having relatively high amplitude at this frequency, and in that the signal processing unit (3) includes a demodula¬ tion circuit (35) connected to said amplication and filter¬ ing means (32,33), for converting the amplified and filtered signal to a direct voltage signal, provided that the am- plified and filtered signal has a characteristic frequency and amplitude distribution corresponding to said normal operational state, and a threshold value detection circuit (41) for sending an output signal to the output unit (5,6,8) when the voltage level of the direct voltage signal attains or exceeds a predetermined threshold voltage value, in which case the output unit (5,6,8) sends a positive operational status indication signal. 2. Detection apparatus as claimed in claim 1, c h a r a c t e¬ r i z e d i n that an integration circuit (38) is connected to said demodulation circuit (35) for forming an envelope sig¬ nal, which is applied to the threshold value detection circuit (41). 3. Detection apparatus as claimed in claim 1 or 2, c h a ¬ r a c t e r i z e d i n that at least one delaying circuit (36,39) is connected between said demodulation circuit (35) and said threshold value detection circuit (41) for eliminating rapid variations in said electrical signal. 4. Detection apparatus as claimed in any one of claims 1-3, c h a r a c t e r i z e d i n that the signal processing unit (3) is adjustable (32,34,37,40) in respect of desired am¬ plification, filter characteristic and/or time delay. 5. Detection apparatus as claimed in claim 4, c h a r a c ¬ t e r i z e d i n that the output unit includes indication means (5) for use in setting the amplification, filter charac¬ teristic and/or time delay of the signal processing unit (3). 6. Detection apparatus as claimed in any one of the preceding claims, c h a r a c t e r i z e d i n that the output unit includes a condition circuit (6) for sending said positive ope¬ rational status indication signal in response to predetermined conditions or sensed states.

Inventors: HEDLUND LENNART, HEDLUND, LENNART
Applicants: HEDLUND LENNART, HEDLUND, LENNART
Application year: 1989
Main classification: G07C3
IPC codes: G01H1, G01H17, G07C3