JPS6156891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a level measuring device equipped with a gain control circuit;
In particular, the present invention relates to a level measuring device having an automatic gain control circuit for so-called gain calibration that controls the gain of a signal amplifier of a minute voltage measuring device such as a field strength measuring device to a predetermined value.

Generally, the gain of a signal amplifier used in a microvoltage measuring device is not constant due to frequency characteristics, temperature characteristics, aging characteristics, and the like. Therefore, in order to perform highly accurate measurements, gain calibration is performed prior to measurement by adding a calibration signal to the signal amplifier and controlling the gain of the signal amplifier so that its output is equal to a predetermined value. is necessary.

FIG. 1 shows the principle of gain calibration conventionally used. In the figure, 1 is a calibration signal generator, 2
3 is a variable gain signal amplifier, 4 is a detection element, 5 is a smoothing circuit, and 6 is an indicator.

During gain calibration, the input switch 2 is switched to the calibration signal generator 1 side manually or by external control.
A calibration signal is applied to a variable gain signal amplifier 3, its output is detected by a detection element 4, smoothed by a smoothing circuit 5, and then sent to an indicator 6. The measurer controls the gain of the variable gain signal amplifier 3 so that the indication on the indicator 6 is equal to a predetermined value. Here, the variable gain signal amplifier 3 changes the gain of the amplifier by, for example, changing the load impedance of the amplifier, or using a variable resistor or varactor in the feedback circuit of the negative feedback amplifier. In this case, the gain is also changed manually.

After the gain calibration as described above is completed, the input switch 2 is switched to the input side and measurement is performed.

In this way, in conventional gain calibration, the input switch 2 is switched and a calibration signal is received.

Check whether the indicated value of the indicator 6 is equal to a predetermined value.

When the instructions are not equal, the gain of the variable gain signal amplifier 3 is controlled.

There are many operation points, such as , which are cumbersome. Furthermore, during the measurement, he accidentally touched the control part of the variable gain signal amplifier 3.

The settings of the control part change due to mechanical vibration or impact.

Problems such as this may occur.

The present invention eliminates such drawbacks and provides an automatic gain control circuit that automatically performs gain calibration of a signal amplifier.

In the present invention, during gain calibration, a staircase wave generator whose output signal sequentially changes stepwise over time is used to control the gain of a variable gain signal amplifier receiving a calibration signal in relation to the staircase wave. When the indicator's indication reaches a predetermined value, the output change of the staircase wave is stopped, and the output value at the time of stopping is maintained. That is, automatic gain calibration can be performed by providing means for changing the gain of the variable gain signal amplifier and maintaining the gain at a constant value.

In the embodiment, the input switch 2 is automatically switched to the input side after automatic gain calibration is completed, and the gain of the variable gain signal amplifier 3 is held constant when measuring the input signal. It is becoming more and more like this.

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3.

In FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals, and their explanations will be omitted. In FIG. 2, 7 is a reference signal generator, 8 is a comparator that compares the output of the smoothing circuit 5 and the reference signal of the reference signal generator 7;
9 is a clock pulse generator; 10 is a switch that operates in conjunction with switch 2 and passes the output of clock pulse generator 9 only during gain calibration; and 11 is a staircase wave generator. Here, the staircase wave generator 11 includes, for example, a binary counter, a plurality of switches controlled by binary signals, a ladder resistor connected to the switches,
and a constant current source. The clock pulse input is counted by a binary counter, and the binary output is used to turn on/off the connection switch between the ladder resistor and the constant current source to control the current value supplied from the constant current source to the load. As a result, it is possible to obtain an output that rises (or falls) stepwise in response to the clock pulse input. Even if you stop adding clock pulses to the binary counter,
Unless you reset the binary counter,
Since the binary signal is preserved, the staircase wave output is also preserved. In the present application, the above functions include the clock pulse generator 9, the staircase wave generator 11 and the switch 1.
This is performed by step-like signal generating means consisting of 0 and 0.

FIG. 3 shows the relationship among the reset signal, clock pulse, binary counter output, and staircase wave output.

During gain calibration, the switch 2 is switched to the side of the calibration signal generator 1 to receive the calibration signal, and at the same time the binary counter that constitutes the staircase wave generator 11 is reset, and then the output of the clock pulse generator 9 is via the switch 10 to the staircase wave generator 11
Add to. Since a stepwise changing signal can be obtained from the output of the staircase wave generator 11, when this signal is used as a gain control signal of the variable gain signal amplifier 3, the gain increases (or decreases) stepwise. For this purpose, the received calibration signal is amplified (or attenuated).
The signal is detected by the detection element 4, smoothed by the smoothing circuit 5, and changes the indication on the indicator 6. Indicator 6
The output of the comparator 8 is made to change when the output of the smoothing circuit 5 when the instruction of becomes equal to a predetermined value and the reference signal of the reference signal generator 7. This stops the generation of clock pulses from the clock pulse generator 9. Instead of stopping the supply of clock pulses, the switching device 10 may be used to stop the supply of clock pulses. As a result, the output of the staircase wave generator 11 is held at a certain value, and the gain of the variable gain signal amplifier 3 is also held at a certain value. Measurement is performed after the gain calibration as described above is completed. During calibration, the switch 2 is automatically switched to the input side, and at the same time, the switch 10 is interlocked so that the clock pulses from the clock pulse generator 9 are Avoid applying it to the wave generator 11. Therefore, even if the detection element 4, smoothing circuit 5, comparator 8, and clock pulse generator 9 operate in the same way as during gain calibration due to the input signal being applied during measurement,
The output of the staircase wave generator 11 does not change, that is, the gain of the variable gain signal amplifier 3 does not change.

Furthermore, during gain calibration, the output of the clock pulse generator 9 is applied to the staircase wave generator 11 after resetting the binary counter that constitutes the staircase wave generator 11, so the output W of the staircase wave generator 11 is the same as before. Regardless of the value at the time of gain calibration, it always changes stepwise from the maximum (or minimum).

Therefore, no matter what intermediate value the gain is set at the time of calibration, the gain of the variable gain signal amplifier 3 can always be made to match the value of the reference signal generator. .

It is also possible to use a voltage holder instead of the staircase wave generator 11, such as a combination of a capacitor and a high input resistance circuit, to charge the gain control signal of the variable gain signal amplifier during gain calibration and continue to hold it during measurement. However, since there is discharge through the capacitor itself and the high input resistance circuit, it is difficult to maintain it for a long time, and the gain must be calibrated frequently.
Therefore, this embodiment is practical, in which the variable gain signal amplifier 3 is controlled using a staircase wave generator, and the gain control signal does not change unless the binary counter is reset.

As explained above, the level measuring device of the present invention has the following features:
During calibration, the gain of the variable gain signal amplifier is automatically controlled using the output of the staircase wave generator, and when measuring the input signal, the gain of the variable gain signal amplifier is kept constant, so the indicated value of the indicator There is no need to check whether is equal to a predetermined value.

Gain control can be performed automatically.

The gain control voltage can be safely maintained even during measurements after gain calibration.

Since there is no indicator reading error, the accuracy of gain calibration is improved.

In addition, for automatic calibration, the gain of the measuring instrument can be calibrated remotely from the measuring instrument by external control.

This effect can be expected.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing gain calibration of a conventional field strength measuring device, FIG. 2 is a system diagram showing an embodiment of the present invention, and FIG. 3 is a system diagram showing the operation of a staircase wave generator. FIG. 1 is a calibration signal generator, 2 is an input switch, 3 is a variable gain signal amplifier, 4 is a detection element, 5 is a smoothing circuit, 6 is an indicator, 7 is a reference signal generator, 8 is a comparator, 9 is a Clock pulse generator, 10 is a switch,
11 is a staircase wave generator, K is a clock pulse, R is a reset signal, and W is an output signal of the staircase wave generator.

Claims (1)

[Claims] 1. Calibration signal generator 1 that generates a calibration signal.
; a variable gain signal amplifier 3 that receives and amplifies the calibration signal; and level conversion circuits 4 and 5 that converts the output signal of the amplifier into a signal corresponding to the output level.
; a reference signal generator 7 that outputs a signal at a preset level; a comparator 8 that receives the outputs of the level conversion circuit and the reference signal generator and detects the level difference; and the level changes sequentially. generating a step-like signal that changes the gain of the amplifier according to the signal, and stopping the change in response to the output signal of the comparator; and when the gain of the amplifier is stopped. The external input signal is measured by the variable gain signal amplifier 3 in which the gain value is maintained. A level measuring device characterized by: 2. The stepped signal generating means 9, 10, 11 are
a clock pulse generator 9; and a staircase wave generator 11 that receives the output signal of the clock pulse generator and generates a step-like signal whose level changes sequentially for changing the gain of the variable gain signal amplifier 3.
2. The level measuring device according to claim 1, further comprising a switch 10 which receives the output signal of the comparator 8 and stops supplying the clock pulse to the staircase wave generator.