JPH0245761Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a self-check device that checks whether there is any abnormality in the operation of each part of a strain measuring instrument.

Generally, in dynamic strain measuring instruments, etc., a carrier wave AC signal output from a carrier wave oscillation circuit is amplified by a bridge voltage amplifier circuit, and a bridge voltage switching circuit having an isolation transformer supplies the required bridge voltage to a measuring bridge, and the output of the bridge is The output of the secondary side of the input transformer is applied to the primary side of the input transformer, and is amplified by a carrier wave amplifier circuit whose gain can be switched according to the measurement range, and detected by a detection carrier filter circuit to remove the carrier wave component. A strain measuring instrument is used in which the measured output is guided to a meter and an output terminal via a DC amplifier circuit and a buffer circuit section.

Conventionally, when trying to check whether or not this type of strain measuring instrument is working properly, it is best to perform a simple temporary measurement using a sensor, or measurement bridge, under normal measurement conditions. I was checking to see if it worked.

However, when checking in this way, even if an abnormality is detected, it is unclear whether the cause lies in the measurement bridge or the strain meter itself (i.e., the measurement bridge is defective, malfunctioning, etc.). The problem was that it was unclear whether there was a problem with the strain meter itself, such as a malfunction.

The present invention was developed in view of these circumstances, and has extremely high noise resistance.No matter what measurement range is set in the measurement mode, the measuring device itself can be easily switched to the check mode. It is an object of the present invention to provide a self-check device for a strain measuring instrument that can reliably and quickly determine the failure of a strain measuring instrument.

In order to achieve this purpose, the present invention
The carrier wave AC signal output from the carrier wave oscillation circuit is amplified by a bridge voltage amplification circuit, and is supplied to the measurement bridge as a required bridge voltage by a bridge voltage switching circuit having an isolation transformer, and the output of the bridge is applied to the primary side of the input transformer. The secondary output of this input transformer is amplified by a carrier wave amplifier circuit whose gain can be switched according to the measurement range, detected by a detection carrier filter circuit, and the carrier wave component is removed.The resulting measurement output is transferred to a DC amplifier circuit. In a strain measuring instrument configured to lead to a meter and an output terminal via a switching circuit, the switching circuit is provided in the bridge voltage switching circuit and forcibly switches the bridge voltage to the maximum voltage in a switching range in response to a check command, and generates a check output. , a check voltage generation circuit that, upon receiving the check output, injects the maximum voltage in the switching range as a check voltage to both ends of a resistor inserted in the middle point of the primary side of the input transformer;
a first resistor substantially equivalent to a measuring bridge for the output terminal of the bridge voltage switching circuit; and a second resistor substantially equivalent to the measuring bridge for the input terminal of the primary side of the input transformer; A first contact connects the first resistor instead of the measuring bridge to the output side of the bridge voltage switching circuit, and connects the second resistor instead of the measuring bridge to the primary side of the input transformer in check mode. Second to do
a third contact that forcibly switches the gain of the carrier wave amplifier circuit to the maximum gain in the check mode regardless of the set measurement range; and a third contact that forcibly switches the gain of the carrier wave amplifier circuit to the maximum gain in the check mode; It has a fourth contact for disconnection and a drive device for driving these first to fourth contacts, and operates these first to fourth contacts in response to an external operation to enter the check mode and to switch off the bridge. The present invention is characterized in that it is equipped with a check control device that gives a check command to the voltage switching circuit.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In the figure, 1 is a carrier wave oscillation circuit that generates a carrier wave AC signal, and 2 is a bridge voltage amplification circuit that amplifies the carrier wave AC signal. 3 is a bridge voltage switching circuit which has an isolation transformer and can switch the bridge voltage by external operation, and in response to a check command input, the bridge voltage is forcibly changed to a predetermined voltage, for example, the maximum of the switching range in this case. A switching circuit is provided for switching the voltage and generating a check output. 4 is a measurement bridge consisting of a resistance bridge using, for example, strain gauges 4a, 4b, 4c, and 4d, and 5 is a measurement bridge in which a resistor 5a is inserted in the middle part (i.e., the midpoint) of the primary coil that receives the output of the measurement bridge 4. An input transformer, 6 is a first resistor approximately equivalent to the measuring bridge 4 for the output of the bridge voltage switching circuit 3, and 7 is a second resistor approximately equivalent to the measuring bridge 4 for the primary side of the input transformer 5. , 8 is a first relay contact consisting of a switching contact that normally connects the measuring bridge 4 to the output terminal of the bridge voltage switching circuit 3 and connects the first resistor 6 only in the check mode; 9 is the input transformer 5; The second relay contact 10 is composed of a switching contact that connects the measurement bridge 4 at all times to the primary side of the switch and connects the second resistor 7 only in the check mode. 11 is a third relay consisting of a switching contact that forcibly switches the gain of the carrier wave amplification circuit 10 to a predetermined value, for example, the maximum gain in this case, regardless of the set measurement range. 12 is a detection carrier filter circuit that detects the output of the carrier wave amplifier circuit 10 and removes the carrier wave component; 13 is a DC amplifier circuit that amplifies the output of the detection carrier filter circuit 12; and 14 is a buffer that receives the output of the DC amplifier circuit 13. 15 is a meter that displays the measured output obtained through the buffer circuit 14, 16 is an output terminal that outputs the measured output to the outside, and 17 is used to normally guide the output of the buffer circuit 14 to the output terminal 16 during check mode. The fourth relay contact 18, which is a normally closed contact that disconnects the relay, has a relay drive circuit for operating the first to fourth relay contacts 8, 9, 11, and 17 in response to an external operation. 1st to 4th
A check control circuit 19 sets the relay contacts 8, 9, 11, and 17 in check mode and gives a check command to the bridge voltage switching circuit 3, and 19 controls the check output output from the bridge voltage switching circuit 3 in response to the check command This is a check voltage generating circuit that responds to the input transformer 5 by injecting a predetermined check voltage between the terminals of the resistor 5a on the primary side.

In such a configuration, when it is desired to perform a check, the check control circuit 18 is operated by an external operation (a check switch, etc. is provided) with the measuring bridge 4 connected and the external device connected to the output terminal. , the first to fourth relay contacts are switched to the check mode, the measuring bridge 4 is disconnected and the equivalent resistors 6 and 7 are connected in its place, the bridge voltage switching circuit 3 becomes the maximum bridge voltage, and the carrier wave amplifying circuit 10 The output terminal 16 is disconnected from the buffer circuit 14, and a predetermined check voltage is injected into the primary side of the input transformer 5. As a result, as long as the main body of the strain measuring instrument (the portion excluding the measuring bridge 4 in the figure) is operating normally, the indication of the meter 15 will be the expected value, and normal operation can be confirmed. If there is an abnormality in the main body of the strain meter, the reading on the meter 15 will not be the expected value. Therefore, it is possible to quickly check whether or not there is an abnormality in the main body of the strain measuring instrument, and if this and the conventional check are used together, it becomes easy to determine the location of the abnormality. Furthermore, in this case, there is also the advantage that an independent check of only the strain measuring instrument body can be performed even when the measurement bridge 4 is connected, when an external device is connected to the output terminal 16, when the output terminal is short-circuited, etc.

The present invention is not limited to the embodiments described above, and can be implemented with various modifications without changing the gist thereof.

For example, the first to fourth contacts may not be relay contacts, but may be ordinary switches, and these switches may be mechanically interlocked by external operation of the check control device.

As described above, according to the present invention, the carrier wave amplifier circuit, the detection carrier filter circuit, the DC amplifier circuit, the meter, and the output terminal are isolated from the measurement bridge by the input transformer, and the bridge voltage switching circuit and the carrier wave oscillation circuit are also isolated. Because it is insulated by a bridge voltage switching circuit with a transformer, it has the advantage of extremely high noise resistance.
This eliminates the inconvenience of not knowing whether the cause of the failure is in the measurement bridge or in the strain measuring instrument body, and it is possible to reliably determine the failure of the measuring instrument body.

In addition, the switching circuit forcibly switches the bridge voltage to the maximum voltage in the switching range according to the check command, and also provides a check output to the check voltage generation circuit. A planned check voltage is injected into the next side, and the gain of the carrier wave amplification circuit is forcibly switched to the maximum gain in the check mode, regardless of the set measurement range, so the above insulation state can be changed. It is possible to surely and quickly check whether or not there is an abnormality in the main body of the strain measuring instrument without requiring any special operation, while maintaining the strain measuring instrument, no matter what measurement range is set in the measurement mode.

In addition, since the check voltage output from the check voltage generation circuit is injected into both ends of the resistor inserted in the circuit at the midpoint of the primary side of the input transformer, when viewed from the measurement bridge, the check voltage is injected. Since the resistor for Even if the in-phase noise voltage induced between the two input lines on the side is superimposed on the check voltage (or measurement output), which is the original signal, the input transformer with a resistor inserted in the middle point Since the noise voltages are balancedly applied to both ends of the next side, the noise voltages are canceled out by the coil of the input transformer, and the noise voltages superimposed on the original signal are removed. In particular, when the two input lines are long, the possibility of noise voltage being mixed in increases, so the above-mentioned noise canceling effect is particularly remarkable, and therefore, it is said that noise resistance can be improved in this respect as well. effective. Incidentally, if the above-mentioned resistor for injecting the check voltage is inserted in a circuit other than the midpoint of the primary side of the input transformer, for example, at the outer end of the coil, and the check voltage is injected into both ends, If the circuit becomes unbalanced by inserting the above resistor into the circuit and a noise voltage of the same phase other than the original signal is mixed in, the magnitude of the noise voltage applied to each end of the primary coil of the input transformer will increase. Because of the difference, only a portion of the cancellation is performed in the primary coil, and the remainder of the cancellation is mixed into the original signal, the check voltage or measured output voltage, as an error.

Also, in the check mode, a first resistor equivalent to the measuring bridge is connected to the output side of each bridge voltage switching circuit instead of the measuring bridge, and a first resistor equivalent to the measuring bridge is connected to the primary side of the input transformer instead of the measuring bridge. Since the configuration is such that an equivalent second resistor is connected, the load conditions are the same, and the presence or absence of a failure can be checked with extremely high accuracy.

Furthermore, since the output terminal is disconnected from the DC amplifier circuit in the check mode, it is possible to reliably eliminate erroneous judgments or checks caused by connection of external equipment.

[Brief explanation of the drawing]

The figure is a block diagram showing the configuration of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Carrier wave oscillation circuit, 2... Bridge voltage amplification circuit, 3... Bridge voltage switching circuit, 4... Measurement bridge, 5... Input transformer, 6, 7... Resistor, 8, 9, 11, 17... ...Relay contact, 10...
... Carrier wave amplifier circuit, 12 ... Detection carrier filter circuit, 13 ... DC amplifier circuit, 14 ... Buffer circuit, 15 ... Meter, 16 ... Output terminal, 1
8...Check control circuit, 19...Check voltage generation circuit.

Claims (1)

[Scope of utility model registration request] The carrier wave AC signal output from the carrier wave oscillation circuit is amplified by a bridge voltage amplification circuit, and is supplied to the measurement bridge as a required bridge voltage by a bridge voltage switching circuit having an isolation transformer, and the output of the bridge is applied to the primary side of the input transformer. The secondary output of this input transformer is amplified by a carrier wave amplifier circuit whose gain can be switched according to the measurement range, detected by a detection carrier filter circuit, and the carrier wave component is removed.The resulting measurement output is transferred to a DC amplifier circuit. In a strain measuring instrument configured to lead to a meter and an output terminal via a switching circuit, the switching circuit is provided in the bridge voltage switching circuit and forcibly switches the bridge voltage to the maximum voltage in a switching range in response to a check command, and generates a check output. , a check voltage generation circuit that, upon receiving the check output, injects the maximum voltage in the switching range as a check voltage to both ends of a resistor inserted in the middle point of the primary side of the input transformer;
a first resistor substantially equivalent to a measuring bridge for the output terminal of the bridge voltage switching circuit; and a second resistor substantially equivalent to the measuring bridge for the input terminal of the primary side of the input transformer; A first contact connects the first resistor instead of the measuring bridge to the output side of the bridge voltage switching circuit, and connects the second resistor instead of the measuring bridge to the primary side of the input transformer in check mode. Second to do
a third contact for forcibly switching the gain of the carrier wave amplifier circuit to the maximum gain in check mode regardless of the set measurement range; and a third contact for forcibly switching the gain of the carrier wave amplifier circuit to the maximum gain in check mode, It has a fourth contact for disconnection and a drive device for driving these first to fourth contacts, and operates these first to fourth contacts in response to an external operation to enter the check mode and to switch off the bridge. 1. A self-check device comprising a check control device that gives a check command to a voltage switching circuit.