JP4484388B2 - Clamp sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a clamp sensor using a zero flux method provided with a demagnetizing circuit, and more particularly, to a clamp sensor in which a degaussing operation is correctly performed.
[0002]
[Prior art]
A clamp sensor is widely used at various measurement sites as a current sensor that can measure the current while keeping the electric wire to be measured in a live state. As an example, a clamp sensor using the zero flux method will be described with reference to FIG.
[0003]
The clamp sensor 300 is openable and closable, and includes a pair of magnetic cores 302 and 302 into which the wire to be measured 301 is inserted. A magnetoelectric converter is disposed in the gap between the base ends of the magnetic cores 302 and 302. The magnetoelectric converter includes a Hall element and a flux gate. In this example, the Hall element 303 is used.
[0004]
In the case of the zero flux method, a negative feedback coil 304 is wound around at least one of the magnetic cores 302 to cancel the magnetic flux generated in the magnetic cores 302 and 302 by the measured electric wire 301. A negative feedback current obtained by amplifying the output voltage by the amplifier 305 is supplied.
[0005]
A voltage detection resistor (output resistor) 307 for detecting a negative feedback current is connected to the negative feedback coil 304, and the detected voltage is amplified to a predetermined level by the amplifier 310 and output to a measuring instrument body (not shown).
[0006]
After the measurement is completed, the wire 301 to be measured is disconnected. However, if there is residual magnetism in the magnetic cores 302 and 302, it may be added to the measured value as an offset during the next measurement.
[0007]
Therefore, this type of clamp sensor is provided with a demagnetization circuit 308. By pressing the demagnetization switch 309 after the measurement is completed, an AC attenuation signal is generated from the demagnetization circuit 308 and supplied to the negative feedback coil 304. Yes. In this example, the negative feedback coil 304 is also used as a degaussing coil, but a dedicated degaussing coil may be provided separately.
[0008]
[Problems to be solved by the invention]
Normally, this degaussing operation must be performed with the wire 301 to be measured removed from the clamp (magnetic core 302). In many cases, such instructions are also included in the instruction manual.
[0009]
Nevertheless, the degaussing switch 309 may be pushed with the wire 301 to be measured inadvertently clamped. Then, the residual magnetism cannot be surely demagnetized and an error occurs during the next measurement. In addition, a current may flow from the clamp side to the measured system due to the demagnetizing current, and in the worst case, the measured system may be destroyed.
[0010]
The present invention has been made to solve such problems, and an object of the present invention is to provide a clamp sensor that allows a user to perform a correct demagnetization operation.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a magnetic core into which a measured electric wire is inserted, a magnetoelectric transducer inserted in a magnetic circuit of the magnetic core, and a negative coil wound around the magnetic core. A feedback coil, an amplifier for amplifying the output voltage of the magnetoelectric converter and supplying a negative feedback current for canceling the magnetic flux to the negative feedback coil, a voltage detection resistor connected to the negative feedback coil, and the negative feedback coil In a clamp sensor based on the zero flux method, which includes a degaussing circuit that supplies a degaussing current to the pin and a degaussing switch that operates the degaussing circuit, an effective value V _{rms of} the output voltage detected by the voltage detection resistor at one input terminal aND circuit but is inputted, taking a comparator reference voltage V _TH is input to the other input terminal, the logical product of the outputs of the degaussing switch the comparator Receives the outputs and the comparator of the degaussing switch and a error display means for performing a degaussing error display under certain conditions, the output of the comparator when the reference voltage V _TH> the effective value V _rms When the output of the demagnetization switch and the output of the comparator are both “H”, the AND circuit drives the demagnetization circuit, and the error display means that the output of the demagnetization switch is “H”. And a demagnetization error display is performed when the output of the comparator is "L".
[0012]
According to this configuration, it is possible to prevent the residual magnetism from being completely degaussed and to prevent an error during the next measurement, and to perform an accurate measurement. It is possible to avoid an adverse effect on the system under measurement that is caused by the flow.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, a clamp sensor shown in the block diagram of FIG. 1 will be described as an embodiment of the present invention. In this description, the notations “H” and “L” are used, but “H” means High (or “1”) of the binary logic signal, and “L” means Low ( Or “0”).
[0014]
The clamp sensor 100 according to this embodiment includes, in addition to the components included in the clamp sensor 300 of FIG. 3 described above, an effective value conversion circuit 101 that converts the output voltage of the amplifier 301 to an effective value, a comparator 102, A product (AND) circuit 103 and an error display means 104 are further provided.
[0015]
In the comparator 102, the effective voltage value V _rms from the effective value conversion circuit 101 is input to one input terminal, the reference voltage V _TH is input to the other input terminal, and the effective voltage value V _rms and the reference voltage V _TH are Are compared and a comparison logic signal is output.
[0016]
In this embodiment, the comparison logic signal of the comparator 102 is set, when the reference voltage _{V TH>} effective voltage _{V rms} at "H", the reference time of the voltage _{V TH} ≦ voltage effective value _{V rms} to be "L" Has been. The equal sign (=) may be placed on the> side, and this point is arbitrary.
[0017]
The reference voltage V _TH is a reference voltage for determining whether or not a current is flowing through the wire to be measured 301, and is set to a value larger than the maximum magnetization of the sensor. As an example, if the sensor rating is an input current of 20 A, an output voltage of 2 V, an output rate of 100 mV / A, and the maximum magnetization of the sensor is equivalent to 20 mA (2 mV in terms of output voltage), the reference voltage V _TH is the maximum The value needs to be larger than the amount of magnetization, and is set to 5 mV in this embodiment.
[0018]
The AND circuit 103 controls the degaussing circuit 308. The switch signal of the demagnetization switch 309 is input to one input terminal of the AND circuit 103, and the comparison logic signal of the comparator 102 is input to the other input terminal. The switch signal is “H” when the degaussing switch 309 is turned on, and is “L” when the demagnetizing switch 309 is turned off.
[0019]
In this embodiment, the error display means 104 includes a D · FF (flip-flop) 105 and a display unit 106. The switch signal of the demagnetization switch 309 is input to one CK (clock) terminal of the D · FF 105, and the comparison logic signal of the comparator 102 is input to the other D (data) terminal. The display unit 106 is connected to the inverted Q terminal of the D · FF 105. FIG. 2 is a truth table of the D · FF 105, and Qn indicates the previous output state of the D · FF 105.
[0020]
Next, the demagnetization operation will be described. When the user turns on the demagnetization switch 309 in an attempt to demagnetize, the switch signal becomes “H”. At this time, if the reference voltage V _TH > the voltage effective value V _rms , the comparison logic signal of the comparator 102 is “H”, so the output of the AND circuit 103 is “H”.
[0021]
As a result, the demagnetizing circuit 308 is driven, and the AC attenuation signal is supplied to the negative feedback coil 304 via the amplifier 305 to demagnetize the magnetic core 302. Since both the CK terminal and D terminal of the D · FF 105 are “H”, the output of the D · FF 105 is “L”, and the display unit 106 is in a non-lighting state.
[0022]
On the other hand, when the demagnetization switch 309 is turned on and the reference voltage V _TH ≦ the voltage effective value V _rms , the comparison logic signal of the comparator 102 is “L”, so that the output of the AND circuit 103 is "L" and demagnetization is not performed.
[0023]
In addition, since the CK terminal of the D · FF 105 is “H” and the D terminal is “L”, the output of the D · FF 105 is changed to “H” and the display unit 106 is turned on, for example, “demagnetization error” is displayed. Made.
[0024]
With this “demagnetization error” display, even if the user turns off the demagnetization switch 309 (switch signal “L”), the error display is maintained until demagnetization is performed in a normal state and both the CK terminal and the D terminal become “H”. Is done.
[0025]
In the above embodiment, a D flip-flop is used for the error display means 104. However, other general-purpose JK flip-flops, a self-holding circuit using a relay, or control software may be used. An alarm buzzer, an alarm lamp, or the like may be used for the display unit. Further, a degaussing dedicated coil may be provided separately from the negative feedback coil.
[0026]
【The invention's effect】
As described above, according to the present invention, demagnetization in a state in which a current flows through the wire to be measured can be prevented by adding a simple circuit in the clamp sensor using the zero flux method.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a clamp sensor according to the present invention.
FIG. 2 is a truth table of D · FF used in the error display means of the embodiment.
FIG. 3 is a block diagram showing a clamp sensor as a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Clamp sensor 101 RMS value conversion circuit 102 Comparator 103 AND circuit 104 Error display means 105 DFF (flip-flop)
106 Display Unit 301 Line to be Measured 302 Magnetic Core 303 Hall Element 304 Negative Feedback Coil 305, 310 Amplifier 307 Voltage Detection Resistance (Output Resistance)
308 Degaussing circuit 309 Degaussing switch

Claims (1)

The magnetic core into which the electric wire to be measured is inserted, the magnetoelectric converter inserted in the magnetic circuit of the magnetic core, the negative feedback coil wound around the magnetic core, and the output voltage of the magnetoelectric converter An amplifier for amplifying and supplying a negative feedback current for canceling the magnetic flux to the negative feedback coil, a voltage detection resistor connected to the negative feedback coil, and a degaussing circuit and the degaussing circuit for supplying a demagnetizing current to the negative feedback coil In the clamp sensor using the zero flux method, which includes a demagnetizing switch for operating the output voltage, the effective value V _rms of the output voltage detected by the voltage detection resistor is input to one input terminal, and the reference voltage V is input to the other input terminal. a _{comparator TH} is input, a logical product circuit for taking a logical product of the output of the comparator output and the degaussing switch, output and the con of the degaussing switch And a error display means for receiving an output of the interpolator performs degaussing error display under certain conditions, the output of the comparator is at "H" when the reference voltage V _TH> the effective value V _rms, the logic The product circuit drives the demagnetizing circuit when both the output of the demagnetizing switch and the output of the comparator are “H”, and the error display means is configured such that the output of the demagnetizing switch is “H” and the comparator A clamp sensor that displays a demagnetization error when the output is "L".

Images