JP2576281B2 - Range switching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a range switching method, and more particularly to a range switching method for automatically setting a range based on a value converted by an A / D converter. It is.

(Prior Art) Conventionally, in an analog circuit having a wide input level, a range setting unit having a plurality of ranges with different gains is provided, and an input signal is taken in an optimum range.
High precision, high linearity output is obtained. The range setting section is usually constituted by an amplifier having a voltage dividing circuit.

The range in the range setting section is generally determined in geometric progression. For example, the range is determined so that the gain changes by one decimal digit. Set the gain of the range setting section to
In order to set the range corresponding to the input value, first set the range setting section to a range that seems appropriate, input the input signal, and in the measurement section, set the output of the range setting section to the predetermined measurement range. If the range of the range setting unit is too large and the output is smaller than the measurement range of the measurement unit, the range of the range setting unit is set to 1
The step is lowered and the output of the range setting unit is determined again, and this is repeated until the output is within a predetermined measurement range, that is, until the output is in an appropriate range. If the output of the range setting section is too small and the output exceeds the measurement range, raise the range of the range setting section by one step.
Repeat the setting until the appropriate range is reached.

As described above, when changing the range of the range setting unit and capturing its output, the input value corresponding to the gain of the range setting unit cannot be obtained in the measuring unit at the same time as the range is switched due to the time constant of the circuit. . For example, in a wide-range DC measuring device using an A / D converter, when the gain is changed by switching the range of the range setting unit, the waiting time until the input value of the A / D converter stabilizes to a constant value is: Circuit
Determined by the time constant of CR, for example, 200ms
It is about. Therefore, conversion must be performed after this waiting time.

Fig. 3 shows A / A with automatic range setting.
6 is a flowchart illustrating an example of an operation of the D conversion device. When the input voltage is applied and the conversion operation starts, first, in Step 21, an initial range setting K is performed. In this case, the largest range is set. After the range is set, the process waits until the above-described waiting time T elapses. After the elapse of the T time, in Step 23, the input voltage by the gain of the range is taken in and A / D conversion is performed.
The converted value V is compared with a predetermined minimum value K _min of the conversion range in Step 24, and if V is smaller than that, the range is lowered by one step in Step 25, and the process loops to Step 22 to repeat the T time. After the waiting time, proceed to Step 23,
Perform A / D conversion. This is repeated, and in Step 24, when the output of the range setting section exceeds the minimum value K _min ,
Move to ep26. In Step 26, the maximum value K _max of the predetermined conversion range is compared with the conversion value V. In the above-described flow, since V does not exceed the maximum value K _max , the process proceeds to Step 28 and the conversion value Is displayed, and the flow ends.

In the above description, the initial range setting K is set to the largest range. However, the initial range setting K may be set to the smallest range. In that case, as long as the condition of Step 26 is satisfied, the loop is repeated while increasing the range one step at a time in Step 27.

Alternatively, the previous range may be stored, and the range in which the initial range setting K is stored may be used. In this case, if the input voltage to be converted next is appropriate for the set range, proceed to Step 28 without changing the range in Step 25 or Step 27.If the range is not appropriate, go to Step 24 or Step 26. Step25 or St depending on conditions
Move to ep27 and repeat the loop until the range setting is appropriate.

In any case, such a conventional method requires a long waiting time every time the range setting is changed, so that there is a problem that a long conversion time is required.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned problems, and has as its object to provide a range switching method capable of performing range setting in a short time. is there.

(Means for Solving the Problems) According to the present invention, an output of a range setting unit to which an input signal is applied is subjected to A / D conversion after a predetermined time has elapsed from the time of range setting, and the converted value is output. Based on the range setting method, the range setting unit changes the range of the range setting unit to the upper or lower range, and repeats the range setting until the output of the range setting unit reaches a predetermined range. A / D conversion is started when a predetermined time that is sufficiently shorter than the time when the input of the D converter stabilizes, and range setting is performed based on the converted value.

(Operation) In a circuit having a time constant, a voltage v appearing in the circuit with respect to an applied voltage V is represented by v = V (1−exp (−t / τ)).

Here, t is an elapsed time after voltage application, and τ is a time constant.

Here, if t is set to a constant value, v = kV, and v and V have a fixed ratio relationship. Therefore, the range can be set by knowing v.

Therefore, Step in the flowchart described with reference to FIG.
Latency in 22 and t, if the maximum value K _max and the minimum value K _min and the k times the value of the comparison voltage at Step24 and Step 26, it is possible to same range setting. The waiting time can be a shorter t time than the T time.

For example, if the above-mentioned waiting time is 200 ms,
If τ (at 7τ, the voltage is 99.91%), then t
Is 20 ms, k is approximately 0.505.

Therefore, the maximum value K _max and the minimum value K _min are each 5
If it is set to 0.5%, the waiting time is 20 ms, which is 1/10 of the conventional one.

Even if t is set to a shorter time, it is sufficient for setting the range. Also in the above specific example, the range setting could be performed in 2 ms.

Embodiment FIG. 1 is a schematic configuration diagram of an A / D converter to which an embodiment of a range switching method according to the present invention is applied. In the figure, 1 is an input terminal, 2 and 3 are switching means, 4 is a gain adjuster comprising an attenuator and an amplifier, 5 is an A / D converter, 6 is a CPU, and 7 is an output terminal. A range setting unit is constituted by the switching circuits 2 and 3 and the gain adjusting unit 4, and the switching means 2 and 3 are controlled by a command from the CPU 6.
Is selected and the gain is set. A / D converter 5
Performs A / D conversion by taking in a voltage for which a gain is set according to a command from the CPU 6.

One embodiment of the range switching method in the A / D converter of FIG. 1 will be described with reference to the flowchart of FIG.

Also in this embodiment, the initial range setting K is set to the largest range. Wait time t in Step2
Is a fixed time sufficiently shorter than the waiting time T described with reference to FIG. 3, as described above. Step4, Step6
Maximum value k _max, the minimum value k _min at the maximum value K _max described in FIG. 3, a k multiple of the minimum value K _min.

The flow of Step2 to Step7 corresponds to Step22 to Step described in FIG.
The same operation as in the flow of Step 27 is performed to complete the range setting according to the input voltage.

Next, the flow of Steps 12 to 17 is entered. This flow is the same as the flow of Steps 22 to 27 described with reference to FIG. That is, in this flow, A / D conversion is performed with a sufficient time T as a waiting time. Therefore,
The conversion accuracy is exactly the same as the conventional one. The converted value is displayed in Step 8, and the flow ends.

The flow of Step 14 to Step 17 is to check whether the set range is appropriate, just in case, and may be omitted. Of course, if the range setting is not appropriate, the range is reset in Step 15 or Step 17, and the A / D conversion is performed after the lapse of T time.

In the flow of FIG. 2 described above, strictly speaking, Step 2
When repeating the loop from Step 5 to Step 5, the A / D converter 5
In some cases, the electric charge charged by the capacitance component remains on the input side of the. Therefore, the influence is exerted in the next loop, but when the range is set from a large range to a small range, the effect is small because the ratio is reduced by the ratio between the ranges. For example, if the range is reduced by one digit for each stage, the voltage due to the remaining charge is only superimposed as 1/10 voltage in the next range.

If a short circuit for discharging the remaining charge is formed before setting the range, the influence can be eliminated.

Further, the time constant in each range may not always be the same. In that case, for each range,
The time t in Step 2 may be set so that k is the same, and a more accurate range setting can be performed.

Further, in the above-described embodiment, the maximum value k _max and the minimum value _kmin in Step 4 and Step 6 are changed to the maximum value K _max , described in FIG.
Although k times the minimum value K _min , in the case of the A / D conversion in Step 3, if an amplifier having a gain of 1 / k times is inserted, the maximum value k _max and the minimum value k _{min in} Step 4 and Step 6 are obtained. _May be the same as the maximum value K _max and the minimum value K _min described in FIG. S
The same applies when the gain in the case of A / D conversion in tep13 is k times.

Regarding the initial setting of the range, it is not always necessary to set the largest range as described with reference to FIG.

(Effects of the Invention) As is clear from the above description, according to the present invention, A /
When there is no need to wait for the D converter input to stabilize before performing A / D conversion, and when a predetermined time that is sufficiently shorter than the A / D converter input stabilization time has elapsed, the A / D conversion Is started, so that the time until the range setting is completed can be shortened.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an A / D converter to which an embodiment of the range switching method of the present invention is applied, and FIG. 2 is a diagram of the range switching method of the present invention in the A / D converter of FIG. FIG. 3 is a flowchart for explaining one embodiment, and FIG. 3 is a flowchart for explaining a range switching method in a conventional A / D converter. 1 ... input terminal, 2, 3 ... switching means, 4 ... gain adjustment section, 5 ... A / D conversion section, 6 ... CPU, 7 ... output terminal.

Claims (1)

(57) [Claims] An output of a range setting unit to which an input signal is applied is subjected to A / D conversion after a predetermined time has passed from the time of setting the range, and the output of the range setting unit is determined based on the converted value. In the range switching method in which the range is changed to change the range to the upper or lower range and the range setting is repeated until the output of the range setting section reaches the predetermined range, the input of the A / D converter is stabilized after the range is set. A range switching method characterized by starting A / D conversion when a predetermined time sufficiently shorter than the time has elapsed, and performing range setting based on the converted value.