JPS6366471A - Level measuring apparatus - Google Patents

Abstract

PURPOSE:To enable the measuring of a level without reinputting of data when an out-of-range is encountered, by providing a second amplifier with a range switching behind a sample holding circuit. CONSTITUTION:An auxiliary range switching circuit 11 is provided between a sample holding circuit 6 and an A/D converter 7. The circuit 11 is made up of a resistance 12, a second operational amplifier 13, resistances 14-1-14-3 for determining an amplification factor thereof 13 and switches 15-1-15-3 to be ON/OFF controlled with a microcomputer 8. At this point, a voltage Vi to be measured is held in the circuit 6 by a sampling pulse SP from the computer 8. Thus, when an out-of-range is encountered, the range of the circuit 11 is switched and the level of the voltage held is measured thereby eliminating the need for reinputting of data.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a level measuring device equipped with range switching, used in the field of optical power meters, digital multimeters, and the like.

"Prior Art" An example of the configuration of a conventional level measuring device of this type is shown in FIG. In this figure, I is an input terminal to which a voltage to be measured Vi is applied, 2 is an input resistor, 3 is an operational amplifier, 4-1. =1
-2. ......4- N is a resistance that determines the amplification factor of the operational amplifier 3, 5-1.5-2', ...5-
Each of N is a switch controlled on/off by the microcomputer 8. 6 is a sample hold circuit that holds the output of the operational amplifier 3 at the timing of the sampling pulse Sp supplied from the microcomputer 8, and 7 is an A/D (analog/digital) conversion that converts the output of the sample hold circuit 6 into digital data. The output data of this A/D converter 7 is supplied to the microcomputer 8.

In the above configuration, the voltage to be measured Vi is amplified by the amplification factor corresponding to the switches 5-1 to 5-N that are turned on at that time in the amplifier 3, and this amplified voltage is applied to the sample and hold circuit 6. Ru. Then, when the microcomputer 8 outputs the sampling pulse Sp,
The output of the amplifier 3 is held by a sample and hold circuit 6, converted into digital data by an A/D converter 7, and supplied to a microcomputer 8.

The microcomputer 8 checks the output of the A/D converter 7, and the value indicates whether the switch 5-1 is currently on.
If it is within the measurement range (in-range) corresponding to 5-H, the output data of the A/D converter 7 is written into the internal memory as the level measurement result. On the other hand, A/D converter 7
If the output data of is outside the measurement range (out range), the microcomputer 8 switches switches 5-1 to 5-5.
H switching (range switching) is performed, then the sampling pulse sp is output, and the output of the amplifier 3 is held again.

"Problems to be Solved by the Invention" As mentioned above, with conventional level measuring devices, if the range is out of range, data must be captured again after changing the range. The data imported into the system was used only for changing the range, resulting in a lot of waste. Furthermore, as shown in Fig. 3, a certain margin Mg is set between each range, but the voltage to be measured Vi changes rapidly, exceeding the margin Mg, as shown in Fig. 3. In this case, if sampling is performed at the point marked O in the figure, a situation will occur in which no data can be captured at all. If data cannot be captured in this way, averaging by software cannot be performed.

Note that in order to suppress fluctuations in the voltage to be measured Vi, it is possible to install a circuit with a large time constant on the input side, but in this case, the measurement must wait for the time of that time constant.
The disadvantage is that the measurement time becomes long.

This invention was made in view of the above-mentioned circumstances, and its purpose is to provide a level measuring device that can measure the level without re-capturing data even when the data is out of range. be.

"Means for Solving the Problems" This invention provides a first
A level measuring device comprising: an amplifier; a sample-and-hold circuit that holds the output of the first amplifier; and an analog/digital converter that converts the output of the sample-and-hold circuit into a digital signal. 2nd one with range switching to amplify the output
A second amplifier is provided, and the output of the second amplifier is applied to the analog/digital conversion circuit.

"Function" According to this invention, the second amplifier with range switching is provided after the sample and hold circuit, so in the case of out-of-range, the held voltage remains unchanged and the range is switched in the second amplifier to measure the level. It can be performed.

"Embodiment" Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. In this figure, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted. The difference between the circuit shown in this figure and the circuit shown in FIG. 2 is that there is an auxiliary range switching circuit between the sample hold circuit 6 and the A/D converter 7! This is the point where l is provided. The auxiliary range switching circuit 11 includes a resistor 12, an operational amplifier I3, resistors 14-1-14-3 that determine the amplification factor of the amplifier 13, and switches 15-1 to 15-1 controlled on/off by the microcomputer 8. 15-3. Note that resistance 2. Amplifier 3. Resistor 4-1 to 4-N, switch 5
Main range switching circuit 1 is a circuit consisting of -1 to 5-N.
It's called 7.

Next, the operation of the circuit shown in FIG. 1 will be explained. First, the microcomputer 8 normally keeps the switch 15-2 on and the switches 15-1 and 15-3 off.

That is, the auxiliary range is set to the second range.

In this state, data is captured in the same manner as in the case described above. That is, the voltage to be measured Vi is amplified by the amplifier 3, and the amplified voltage is used as the sampling pulse S output from the microcomputer 8.
It is held in the sample hold circuit 6 based on p. This held voltage is further amplified by the amplifier 13. In this case, the amplification factor is 12 resistors and 1 resistor.
Determined by the value of 4-2. The output of the amplifier 13 is then converted into digital data by the A/D converter 7 and supplied to the microcomputer 8. and,
If the data is in-range, it is written to the memory within the microcomputer 8 as a level measurement result. On the other hand, if the data output from the A/D converter 7 is out of range, the microcomputer 8 turns off the switch 15-2, and also turns off the switch 15-2.
1 or! 5-3 is turned on. That is,
Switches the auxiliary range. This changes the measurement range. The microcomputer 8 checks the output of the A/D converter 7 again, and if it is in range, reads it into the internal memory. Then, at the time of the next measurement, the microcomputer 8 again switches the switch 15-1 to
．． 15-3 is turned off, switch 15-2 is turned on, and switches 5-1 to 5-N (main range changeover switches) are set to the expected range.

According to the above embodiment, the range M-1 to M+1 can be measured in one sampling. Further, if the linearity of the amplifier is ideal, the entire range can be covered by setting the number of stages of the auxiliary range switching circuit 11 to N, which is the same as the number of stages of the main range switching circuit 17.

Further, since averaging can be performed over the entire range by software, fluctuations can be suppressed simply by increasing the number of times of averaging. Furthermore, it is possible to adjust the number of times of averaging according to level fluctuations.

"Effects of the Invention" As explained above, according to the present invention, since the second amplifier with range switching is provided to amplify the output of the sample and hold circuit, sampled data is wasted due to range switching. Never. Further, according to the present invention, since data can always be captured, by increasing the number of times of averaging by software, highly accurate measurements can be performed over the entire range.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a circuit diagram showing an example of the configuration of a conventional level measuring device.
This figure is a waveform diagram for explaining the problems of the level measuring device shown in FIG. 2. 3... operational amplifier (first amplifier), 6...
. . . Sample hold circuit, 7 . . . A/D converter, 13 . . . Operational amplifier (second amplifier).

Claims (1)

[Claims] a first amplifier with range switching that amplifies the input signal;
In a level measuring device comprising a sample and hold circuit that holds the output of the first amplifier and an analog/digital converter that converts the output of the sample and hold circuit into a digital signal, the output of the sample and hold circuit is amplified. A level measuring device characterized in that a second amplifier with range switching is provided, and the output of the second amplifier is applied to the analog/digital conversion circuit.