GB2347501A

GB2347501A - Device for measuring noise

Info

Publication number: GB2347501A
Application number: GB9904694A
Authority: GB
Inventors: Ching-Shen Hong
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-03-01
Filing date: 1999-03-01
Publication date: 2000-09-06
Also published as: GB9904694D0; DE29903728U1

Abstract

The invention relates to a device for measuring noise, which uses a sensor circuit (2) to detect the noise source. The sensor circuit (2) has two sensors (21,22) which both can detect the ambient noise. A noise source to be tested is placed in front of one of the sensors. The output of the sensor circuit (2) is connected to the input of the circuit for eliminating ambient noise (3) and then the ambient noise is eliminated by said circuit. The noise signal without ambient noise is connected to a signal processing circuit (4) and is processed suitably to determine whether the noise is acceptable or not. A device for eliminating ambient noise is also described.

Description

TITLE DEVICE FOR MEASURING NOISE BACKGROUND OF THE INVENTION (1) Field of the Invention: The invention relates to a device for measuring noise, particularly to a device for measuring noise generated by a fan.

(2) Description of the Related Art When measuring a noise source, the sensor will detect the ambient noise and the real noise from the source. The measured value including ambient noise is incorrect.

It is necessary to install an anechoic room for eliminating the interference of the ambient noise. The equipment for measuring noise must be placed into the an anechoic room in order to isolate the outer noise. However, the cost of installing such an anechoic room is very high. Therefore, the invention provides a novel device for measuring noise such that the real noise can be correctly measured, not including the ambient noise.

SUMMARY OF THE INVENTION An object of the invention is to provide a device for measuring noise so that the real noise can be correctly measured with a low cost, simple and precise device.

Another object of the invention is to provide a device for measuring noise so that the ambient noise can be eliminated by a low cost, simple and precise device without needing an expensive anechoic room. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a circuit block diagram according to the invention.

Fig. 2 is a diagram illustrating operation of the sensors according to the invention.

Fig. 3 is a circuit diagram illustrating the connection of the sensors and circuit for eliminating ambient noise according to the invention.

Fig. 4 is a circuit diagram illustrating connection of the signal rectifier circuit and DC amplifier circuit according to the invention.

Fig. 5 depicts a comparator circuit according to the invention.

Fig. 6 depicts a result display circuit according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Described in the embodiment of the invention is a device to measure the noise from a fan. Fig. 1 is a circuit block diagram according to the invention. A device for measuring noise comprises: sensor circuit 2, circuit for eliminating ambient noise 3 and signal processing circuit 4. Referring to Fig. 2, the sensor circuit 2 comprises two sensors 21 and 22 which can all detect ambient noise. The fan 11 under test is mounted before the sensor 21. The sensors are the professional capacitor type microphones with high precision and sensibility, or are moving coil type microphones with low impedance, high precision and sensibility. However, the sensors have the characteristic of high gain and low noise.

The output of sensor circuit 2 is connected to the input of circuit 3 for eliminating ambient noise. Because both of the sensors 21 and 22 can detect the ambient noise, the ambient noise can be eliminated by inverting the phase of the value of the ambient noise from one of the sensors and adding the value of the ambient noise from the other sensor. Thus, the ambient noise can be eliminated through the circuit for eliminating ambient noise. In addition, a differential circuit can be used as the circuit for eliminating ambient noise. Because both of the sensors 21,22 can detect the ambient noise, the ambient noise is directed to a common mode signal. Therefore, the common mode ambient noise can be eliminated by a differential circuit.

The signal processing circuit 4 determines whether the noise is acceptable or not by suitably processing the eliminated ambient noise. The signal processing circuit 4 comprises a signal rectifier circuit 41, a DC amplifier circuit 42, a comparator circuit 43 and a result display circuit 44. The fan noise signal which does not comprise ambient noise is rectified into a DC noise signal by the signal rectifier circuit 41. The DC amplifier circuit 42 amplifies the DC noise signal. The amplitude of the amplified DC noise signal is proportional to the real noise. The comparator circuit 43 provides a reference level. When the amplified DC noise signal is greater than the reference level, there is a output signal indicating that the noise is not acceptable. The result display circuit 44 shows whether the fan noise is acceptable or not.

In order to further understand the invention, the circuit diagrams are described as follows. Fig. 3 is a circuit diagram depicting the sensors circuit and circuit for eliminating ambient noise according to the invention. Two cases are discussed as follows.

(1) When the ambient noise appears, both of the sensors 21 and 22 in Fig. 3 detect the ambient noise, then the same ambient noise signal is amplified by operational amplifiers 31 and 32. For instance, the ambient noise signal (eO) is detected by sensor 21 and sensor 22 respectively and then passes through the operational amplifier 31.

The resistor 33 is equal to the resistor 34 ; therefore, the output of the operational amplifier 31 is (-eO). The output of the operational amplifier 31 is connected to the point (A) through resistor 35. The sum of signal (-eO) and the signal (eO) from the sensor 22 is zero, so the voltage on the point (A) is zero given by eO + (-eO) = 0. The output of the operational amplifier 32 is still zero (e2 = 0) even the signal on the point (A) passes through the operational amplifier 32. Thus, the ambient noise signal (eO) is eliminated.

(2) The fan 11 is mounted before sensor 21. The fan noise signal through the operational amplifier 31 is outputs to the point (A). The voltage on the point (A) is ( el). The sensor 22 can not detect the fan noise, so the fan noise signal from the sensor 22 is zero. The voltage on the point (A) is (-ex) +0, and thus equal to (-el). The signal (-el) through the operational amplifier 32 is amplified into (e2) which does not include the ambient noise.

Fig. 4 depict the signal rectifier circuit and the DC amplifier circuit. Referring to Fig. 4, the full-wave rectification is achieved by the operational amplifier 51. The input of the operational amplifier 51 is connected to the output signal (e2) of the operational amplifier 32 in Fig. 3, which is an AC signal. The resistor 52 and resistor 53 are the the gain control resistors. The resistor 54 and resistor 55 function as the bias of the operational amplifier 51 so that the AC signal can be full-wave rectified without any cut off which results in incorrect result. The capacitor 56 functions as a filter for bias so as to provide a smooth bias for the operational amplifier 51. The diodes 57 and 58 function as rectifier diodes. The rectified DC voltage is amplified and filtered through the operational amplifier 59, then the smooth DC voltage output (e3) is obtained.

Fig. 5 shows a comparator circuit diagram according to the invention. The amplitude of the voltage (e3) from the output of the operational amplifier 59 is proportional to the real noise. The greater the noise is, the greater the DC voltage (e3) is obtained. The lower the noise is, the lower the DC voltage (e3) is obtained. In Fig.

5, there is a adjustable reference voltage for determining whether the noise is acceptable. The signal (e3) is the input voltage in the Fig. 5. The operational amplifier 61 functions as a comparator. The adjustable resistor 62 can set a DC voltage level (Vref) under that the fan noise is acceptable. When e3 > Vref, the operational amplifier 61 outputs a DC voltage. Thus, the greater the value of e3 > Vref is, the greater the output of the operational amplifier 61 outputs proportionally. The operational amplifier 63 functions as a buffer for the output DC voltage. When the signal (e3) is greater than the reference voltage, the circuit outputs the result (e4) and the signal (e4) is proportional to the noise. When the signal (e3) is lower than the reference voltage, the circuit outputs the result (e4=0). It can be determined whether the noise is acceptable based on the signal (e4).

Fig. 6 depicts a result display circuit according to the invention. According to the amplitude of the signal (e4), the LEDs 71, 72,73,74 or 75 sequentially lights. When the signal (e4) is smallest, the LED 71 light. Alternatively, when the signal (e4) is largest, the LED 75 lights. The LEDs 71,72 and 73 display green to represent that the noise of the fan is acceptable. The LED 74 displays yellow to represent that the noise of the fan is not acceptable, but still marginally acceptable. The LED 75 displays red to represent that the noise of the fan is too large to be acceptable. One can see whether the noise is acceptable or not by the color shown on the LED.

The invention also provides a device for eliminating ambient noise. Thus, there is no need for the expensive anechoic room. The device for eliminating ambient noise can eliminate the ambient noise by a low cost, simple and precise device which comprises: a sensor circuit and a circuit for eliminating ambient noise. The sensor circuit comprises two sensors, and both of the sensors can detect ambient noise. In the operation, the noise source is placed in front of one of the sensors. The sensors are professional capacitor type microphones with high precision and sensibility, or moving coil type microphones with low impedance, high precision and sensibility, and further have the characteristics of high gain and low noise. In operation, the input of the circuit for eliminating ambient noise is connected to the output of the sensor circuit so as to eliminate ambient noise. Because both of the sensors can detect the ambient noise, the ambient noise can be eliminated by inverting the phase of the value of the ambient noise from one of the sensors and then adding the value of the ambient noise from the other sensor. In addition, a differential circuit can be used to function as the circuit for eliminating ambient noise. Because both of the sensors can detect the ambient noise, the ambient noise is a common mode signal. Therefore, the common mode ambient noise can be eliminated by a differential circuit.

According to the invention, the device for measuring the noise can be implemented by a low cost, simple and precise electronic circuit. There is no need to establish an expensive anechoic room and the circuit according to the invention can correctly measure the noise, and eliminate the interference of the ambient noise.

Claims

1. A device for measuring noise comprising : a sensor circuit having two sensors to detect ambient noise, wherein a noise source to be tested is placed in front of one of the sensors; a circuit for eliminating ambient noise, wherein an input terminal of said circuit is connected to an output of the sensor circuit; and a signal processing circuit suitably processing the noise except the eliminated ambient noise to determine whether the noise is acceptable or not.

2. The device as claimed in Claim 1, wherein the sensors are professional capacitor type microphones with high precision and sensibility.

3. The device as claimed in Claim 1, wherein the sensors are moving coil type microphones with low impedance and high precision and sensibility.

4. The device as claimed in Claim 1, wherein the circuit for eliminating ambient noise inverts the phase of the ambient noise from one of the sensors, then adds the ambient noise from the other sensor therein so as to eliminate ambient noise.

5. The device as claimed in Claim 1, wherein the circuit for eliminating ambient noise is a differential circuit which eliminates common mode ambient noise from the two sensors.

6. The device as claimed in Claim 1, wherein the signal processing circuit comprises: a signal rectifying circuit for rectifying an eliminated ambient noise signal into a DC noise signal; a DC amplifier circuit for amplifying the DC noise signal; a comparator circuit having a reference level for comparing an amplified DC noise signal to output a signal indicating that the noise is not acceptable when the amplified DC noise signal is greater than the reference level.

7. A device for eliminating ambient noise comprising: a sensor circuit having two sensors to detect ambient noise, wherein a noise source to be tested, is placed in front of one of the sensors; and a circuit for eliminating ambient noise, wherein an input terminal of said circuit connected to an output of the sensor circuit

8. The device as claimed in Claim 7, wherein the sensors are professional capacitor type microphones with high precision and sensibility.

9. The device as claimed in Claim 7, wherein the sensors are moving coil type microphones with low impedance and high precision and sensibility.

10. The device as claimed in Claim 7, wherein the circuit for eliminating ambient noise inverts the phase of the ambient noise from one of the sensors, then adds the ambient noise from the other sensor therein so as to eliminate ambient noise.

11. The device as claimed in Claim 7, wherein the circuit for eliminating ambient noise is a differential circuit which eliminates common mode ambient noise from the two sensors.

12. A device for measuring noise, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.