JPH05281361A - Radiation monitor - Google Patents

Abstract

PURPOSE:To obtain a radiation monitor which can withstand against external noise and in which a highly reliable countermeasure is taken against noise. CONSTITUTION:The title monitor is constituted by separately providing a radiation detector 1, preamplifier 2, and monitoring unit 3 and connecting them to each other through signal cables 4 each of which is constituted in such a way that a signal line 4a having a signal potential is shielded with a common circuit 4b having a common potential. In addition, the monitor is provided with a noise filter 6 which is connected between the common circuits 4b on the input and output sides of the amplifier 2 and makes high-frequency noise to flow to the earth, noise filter checker 8 for confirming the soundness of the filter 6, and filter check switching means 7 which is installed to the common circuit 4b on the input side of the unit 3 and connects the circuit 4b to the earth at the time of detecting radiation or to the checker 8 at the time of checking the soundness of the filter 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation monitor used in a nuclear power plant, a nuclear reactor fuel reprocessing facility, a radioactive substance handling facility, and the like, and particularly to the influence of electromagnetic induction noise received from a motor or the like during radiation detection. Radiation monitor that can eliminate

[0002]

2. Description of the Related Art Generally, a fixed radiation monitor is used for radiation monitoring of a nuclear power plant, a nuclear reactor fuel reprocessing facility, a radioactive material handling facility, and the like. This radiation monitor normally employs a method of collectively and continuously monitoring the radiation detected at various places in the facility by a monitoring unit installed in the central control room.

FIG. 4 is a diagram showing the structure of a conventional radiation monitor. This monitor includes a radiation detector 1 for detecting a radiation dose, a preamplifier 2 for amplifying a weak signal output from the radiation detector 1, and a signal from the preamplifier 2 for processing as a radiation level. The monitoring unit 3 and the monitoring unit 3 are connected to each other by a signal cable 4.

In the radiation monitor having the above structure, when a spark signal or the like is generated from a motor or the like near the signal cable 4, the spark signal is induced in the signal cable 4, and the spark signal becomes noise and becomes a detection signal. There is a problem that adversely affects. Therefore, conventionally, the following noise avoidance technique has been considered from the viewpoint of avoiding the adverse effect of the electromagnetic induction noise. (B) A configuration in which noise suppression for noise suppression is provided on the noise generation side.

(B) As the signal cable 4, a coaxial cable in which the outer side of a signal line 4a for transmitting a detection signal is covered with a common circuit 4b grounded to earth as shown in FIG. (C) Similarly, as shown in FIG. 4, the signal cable 4 is covered with a metal conduit tube 5 to electromagnetically shield it from noise sources. (D) Further, there is a type that employs an isolation amplifier that separates the common circuit 4b.

[0006]

However, it is difficult to completely eliminate the adverse effects of noise in each of the radiation monitors described above. That is, it is difficult to identify the noise source in the technique (a), and a noise current may flow to the input side of the preamplifier 2 in the technique (b). Also,
The technique of (C) is very effective for electrostatic induction (C couple) mixed by stray capacitance between the conduit 5 and the device or between the conduit 5 and the signal cable 4, but the internal signal It has almost no effect on the noise generated when the magnetic flux is coupled to the loop formed by the cable 4. Moreover, other than iron tubes, tin tubes, aluminum tubes and copper tubes are less effective.

Further, in the technique (d), when the ground is cut off between the devices by using the isolation amplifier, the influence of the interlinkage magnetic flux due to the formation of the closed loop which causes the noise at the two-point grounding and the difference in the ground potential. Although it can prevent the effects, signal line 4
Resistance of a, input impedance and common circuit 4b
There is a problem that noise will intrude unless the AC bridge circuit constituted by the resistance component of, the input impedance, and the stray capacitance entering in parallel with each input impedance satisfies the balance condition.

Other than this, noise may be induced by causing a difference in stray capacitance with respect to the ground due to unbalance of the signal cable 4 itself, wiring of a very short length not using the signal cable 4 and circuit unbalance. .. The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a radiation monitor which is resistant to noise received from the outside and has a highly reliable noise countermeasure.

[0009]

In order to solve the above problems, the present invention provides a radiation detector for transmitting a weak signal corresponding to a radiation dose, a preamplifier for amplifying the weak signal, and this preamplifier. A monitoring unit that processes the amplified signal from the device and outputs a radiation level, and the radiation detector, the preamplifier, and the monitoring unit are installed at a required distance apart from each other, and signals are respectively sent between these devices. In a radiation monitor connected by a signal cable covered with a common circuit that has a common potential for shielding the signal line that transmits the signal, a high-frequency noise that is connected between the input side and output side common circuits of the preamplifier Noise filter to check the soundness of this noise filter and the input of the monitoring unit And a filter check switching unit that connects the common circuit to the ground when detecting radiation and connects the common circuit to the noise filter checker when checking the soundness of the noise filter. It is a monitor.

[0010]

Therefore, according to the present invention, by taking the above-mentioned means, at the time of radiation detection, high-frequency noise entering from the outside into the common circuit of the signal cable flows to the ground through the noise filter, and this noise filter When checking, the noise filter checker uses the common circuit of the signal cable to check the soundness of the noise filter, so the signal can be protected from the effects of external noise, while the soundness of the noise filter can be checked when necessary. it can.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a radiation monitor according to the present invention. In the figure, the same parts as those in FIG. 4 are designated by the same reference numerals and the description thereof is omitted. That is, in FIG. 1, a noise filter 6 is provided between the input side and output side common circuits 4b of the preamplifier 2 in FIG. 4 to protect high frequency noise from the outside from affecting the signal line 4a. Further, a filter check switching means 7 is provided in the input side common circuit 4b of the monitoring unit 3, and the earth line and the noise filter checker 8 can be selected by the filter check switching means 7.
When selecting the noise filter checker 8, the noise filter 6
It is configured to check the soundness of.

A capacitor or the like is used as the noise filter 6, and the common circuit 4b is AC-grounded at the input point side of the preamplifier 2. When high frequency noise such as electromagnetic induction noise enters the common circuit 4b from the outside, it can flow to the ground through the noise filter 6.

The filter check switching means 7 connects the common circuit 4b to the ground when detecting radiation, and connects the common circuit 4b to the noise filter checker 8 when confirming the soundness of the noise filter 6.
Connect to.

The noise filter checker 8 has a function of confirming the soundness of the noise filter 6. Here, assuming that the soundness of the noise filter 6 is, for example, the capacitance of the capacitor, the noise filter checker 8 is a capacitance meter, and for example, a standard capacitance capacitor is provided inside.
It has a bridge circuit consisting of a variable resistor and a galvanometer and a high frequency power supply connected to this bridge circuit, and the capacitance is checked by the balance condition of the bridge with a noise filter (capacitor) 6 added to one side. There is.
The operation of the radiation monitor having such a configuration will be described.

First, the operation when detecting radiation will be described. The radiation detector 1 converts the detected radiation into a weak current according to the dose, and sends it to the preamplifier 2 via the signal cable 4. The preamplifier 2 amplifies this weak current and sends a signal to the monitoring unit 3 via the signal cable 4 on the output side. The monitoring unit 3 outputs the radiation level based on this signal.

When noise is generated in the vicinity of the signal cable 4 in the series of detection processes, the high frequency noise is superimposed on the common circuit 4b of the signal cable 4 as a noise current by electromagnetic induction. The noise filter 6 connected to the common circuit 4b causes high frequency noise, which affects the signal line, of the noise current to flow to the ground, so that the noise does not enter the preamplifier 2.

Next, the operation for checking the soundness of the noise filter 6 will be described. Here, the noise filter 6 is used as a capacitor, and the noise filter checker 8 is used.
Will be described as a capacitance meter. The soundness of the noise filter 6 means the capacitance value of the capacitor.

First, the filter check switching means 7 is switched from the ground side to the noise filter checker 8 side. Therefore, the noise filter checker 8 is connected to the common circuit 4b of the signal cable 4 and the noise filter 6 via the filter checker switching means 7. By this connection, the noise filter 6 and the noise filter checker 8 form a bridge circuit with each other. The capacitance of the noise filter 6 is measured by changing the variable resistance of the noise filter checker 8 so that the balance condition of this bridge circuit is satisfied.

If the capacitance measured at this time is within the error range compared with the predetermined capacitance value, the noise filter 6
Is regarded as normal and the filter check switching means 7 is switched to continue monitoring radiation.

Therefore, according to the above embodiment, the high frequency noise current affecting the common circuit 4b of the signal cable 4 flows to the ground by the noise filter 6 and does not reach the preamplifier 2. No output.
Therefore, the radiation monitor can be electromagnetically shielded from the noise source.

More specifically, since the common circuit 4b of the radiation monitor signal cable 4 is connected to the ground on the monitoring unit 3 side, the noise current induced in the common circuit 4b will be affected if it is sent to the ground. It disappears, but if it is grounded at the preamplifier 2 side
It becomes a point ground and is easily affected by the ground potential difference. Therefore, the noise current flows into the ground on the monitoring unit side or the input side of the preamplifier 2, but the noise current does not flow into the preamplifier 2 because the noise filter 6 is inserted in the preamplifier 2 side.

Further, when the noise filter 6 fails for some reason, this failure causes a two-point grounding in the short-circuit mode, and a new noise due to the influence of the interlinkage magnetic flux due to the formation of the closed loop or the influence of the ground potential difference. Therefore, it is necessary to check the soundness of the noise filter 6, but the filter check switching means 7 on the monitoring unit 3 side.
Switch the noise filter checker (capacitance meter) 8
Since the capacity of the noise filter (capacitor) 6 is regularly checked by the above, the soundness of the noise filter 6 can be confirmed remotely without a special cable.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a diagram showing the configuration of the noise filter. As illustrated, the common circuit 4b of the signal cable 4 is grounded via a plurality of series capacitors as a noise filter. Therefore, even if one capacitor fails and enters the short-circuit mode, the common circuit 4b is AC-grounded by the other capacitor. Second mentioned above
According to this embodiment, since the noise filter 6 is formed by connecting a plurality of capacitors in series, it is possible to eliminate the influence of the failure of the capacitors.

Further, a third embodiment of the present invention will be described. FIG. 4 is a diagram showing a configuration in which the noise filter checker is also used as a calibration transmitter. That is, the monitoring unit 3 is calibrated by inputting a predetermined high frequency current from the noise filter checker (capacitance meter) 8 to the monitoring unit 3 as a radiation detection signal.

In the third embodiment, since the high frequency current of the capacitance meter is used as the calibration signal of the monitoring unit 3, the radiation monitor can be calibrated and the reliability of the radiation monitor is improved. The present invention is not limited to the embodiments described above and shown in the drawings, and various modifications can be carried out without departing from the scope of the invention.

[0026]

As described above, according to the present invention, at the time of detecting radiation, the noise filter causes high-frequency electromagnetic induction noise externally applied to the common circuit of the signal cable to flow to the ground, and at the time of checking the noise filter, Since the noise filter checker confirms the soundness of the noise filter using the common circuit of the signal cable, it is possible to provide a radiation monitor that is highly resistant to external noise and has a highly reliable noise countermeasure.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a radiation monitor according to the present invention.

FIG. 2 is a diagram showing another embodiment of the noise filter according to the present invention.

FIG. 3 is a diagram showing another embodiment of the noise filter checker according to the present invention.

FIG. 4 is a diagram showing a configuration of a conventional radiation monitor.

[Explanation of symbols]

1 ... Radiation detector, 2 ... Preamplifier, 3 ... Monitoring unit, 4 ... Signal cable, 4a ... Signal line, 4b ... Common circuit, 5 ... Conduit, 6 ... Noise filter, 7 ... Filter check switching means, 8 … A noise filter checker.

Claims (1)

[Claims] 1. A radiation detector for transmitting a weak signal according to a radiation dose, and a preamplifier for amplifying the weak signal,
A monitoring unit that processes the amplified signal from the preamplifier and outputs a radiation level, and the radiation detector, the preamplifier, and the monitoring unit are installed at a required distance apart from each other, and each of these devices is installed. In a radiation monitor that is connected by a signal cable covered with a common circuit that has a common potential for each device that shields the signal lines that transmit signals between them, and that connects between the common circuits on the input side and output side of the preamplifier A noise filter that sends high-frequency noise to the ground, a noise filter checker that checks the soundness of this noise filter, and a common circuit on the input side of the monitoring unit. When connecting and checking the soundness of the noise filter, connect the common circuit to the Radiation monitor characterized by comprising a filter check switching means connected to the noise filter checker.