JPS5940662Y2 - digital computing device - Google Patents

Description

[Detailed description of the invention] This invention is a digital computing device that handles analog input and analog output using a digital-to-analog conversion circuit that combines a current-voltage conversion circuit using an operational amplifier and a multiplier current output type digital-to-analog converter. In particular, the purpose of the present invention is to make it possible to effectively demonstrate its functions by using it for industrial measurement control.

In a conventional analog input/output digital arithmetic unit of this type, for example, as shown in FIG.

- The digital signal is converted into an analog current by the multiplier current output type digital-to-analog converter 13, the conversion output is converted to voltage by the operational amplifier 14, and the converted analog voltage is the other input side of the comparator 12. ~Supplied.

The comparator 12 compares the magnitude of the two forces, one-bit addition or subtraction is performed in the microcomputer 15 depending on the polarity of the output, and the result of the calculation is input to the digital-to-analog converter 13.

The process input from the multiplexer 11 is converted into a digital signal by applying such operating force.

Furthermore, the difference between the process input input to the microcomputer 15 in this way and, for example, a set value is calculated within the microcomputer 15 as necessary, and proportional calculations and integral calculations are performed according to the difference. The result is converted into an analog current by a digital-to-analog converter 13, and further converted into an analog voltage by an operational amplifier 14.

The warp-converted analog voltage is held in the m conversion holding circuit 16 under the control of the computer 15, and is thereby outputted as a process output and used, for example, in a signal method for controlling an operating valve.

In this way, the digital-to-analog converter 13 and the operational amplifier 14 are combined to perform digital-to-analog conversion and convert an analog input into a digital signal.

Alternatively, a digital signal is converted into an analog output.

In this case, the relationship between the digital input Di of the digital-to-analog converter 13 and the analog output Ao of the operational amplifier 14 is as shown by the straight line 17 in FIG.
is zero, the analog output AO is zero, and based on this point, the analog output Ao corresponds to the digital human power Di.
changes linearly.

However, in the field of industrial measurement and control, signals biased by a constant value, such as 1 to 5 V or 4 to 20 mA, are often used as signals representing process quantities.

In addition, in order to ensure the closing and opening of operation valves, etc., the process output is O65~5.5V, 2~22mA, etc.
A so-called over-range signal, which is extended vertically with respect to 5V and 4 to 20mA, is output.

When the digital arithmetic unit shown in Fig. 1 is used in such a field, the converter itself converts 0-D3 into A.

-A3, but the conversion between 0-D and 0-A2 is not utilized, and the conversion range is not utilized effectively.

Also, if you want to overrange, use the digital input 0-D.
3 is possible, so the output A1 is smaller than A2
In other words, it is possible to extend the range downward, but it is not possible to convert an input larger than the digital input D3. Therefore, as shown by the dotted line 18 in Figure 2, the conversion characteristics are changed and the digital The range was expanded upward by increasing the weight per 1 bit of input so that a value A larger than A could be obtained as an analog output for the maximum digital human power D3.

This has the disadvantage that the resolution of the digital-to-analog conversion decreases.

In this invention, a certain bias is added to the operational amplifier that constitutes the current-voltage conversion circuit that converts the conversion output of the multiplier current output type digital-to-analog converter into voltage output.
Shift its operating point.

In this way, the maximum resolution of digital-to-analog conversion can be maintained, the conversion range can be effectively utilized, and the conversion range can be expanded not only to the lower side but also to the upper side.

The constant bias mentioned above is because the multiplier current output type digital-to-analog converter has a built-in stable reference voltage source.

By utilizing this, a stable and accurate voltage can be easily obtained.

For example, as shown in FIG. 3 by assigning the same reference numerals to the parts corresponding to those in FIG. The other input side of the operational amplifier 14 is not grounded, but is connected to the mover of a variable resistor 19, one end of which is grounded, and the other end connected to a reference built in the digital-to-analog converter 13. Connected to a voltage source.

In this way, a constant bias is applied to the operational amplifier 14 from the movable element of the variable resistor 19, and its operating point is shifted.

For example, as shown by the straight line 21 in FIG.
The movable element of the variable resistor 19 is adjusted so that when i is zero, an analog output A3 of, for example, 0.5V is output.

Therefore for maximum digital input D3. Asalog output A4
, in this example, 5.5V is output.

In other words, the conversion lens extends not only downward but also upward,
Moreover, the slope of this straight line 21 is the same as that of the straight line 17 in FIG. 2, so that range expansion is achieved with maximum resolution.

As mentioned above, according to the digital arithmetic unit of this invention,
For example, when converting an analog input biased to a constant value such as 1 to 5 V or 4 to 20 mA to digital, the conversion characteristics of the digital-to-analog converter 13 can be effectively utilized.

Further, when a digital signal is output as an analog output, the range can be expanded without reducing the resolution of the digital-to-analog converter 13.

In order to apply a constant bias to the operational amplifier 14, a constant voltage source may be provided without being limited to the above example.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional analog input/output digital processing device, Fig. 2 is a warpage conversion characteristic diagram, Fig. 3 is a block diagram showing an example of an analog input/output digital processing device according to this invention, and Fig. 4 is a block diagram showing an example of the analog input/output digital processing device according to the invention. It is a figure which shows an example of the conversion characteristic. 12... Comparator, 13... Multiplying current output type digital-to-analog converter, 14... Operational amplifier for current-voltage conversion, 15... Microcomputer. , 16... Sampling holding circuit, 19...
...Variable resistor for bias.

Claims (1)

[Scope of utility model registration request] A microcomputer that calculates a human-powered signal and outputs a calculated digital signal; a digital-to-analog converter that outputs an analog current signal by converting the digital signal from the microcomputer into a digital-to-analog converter; and this digital-to-analog converter. A current-voltage conversion circuit consisting of an operational amplifier to which a current signal of is applied to one input terminal and a shift means for shifting its operating point is connected to the other input terminal; The present invention is characterized by comprising a comparator that compares the output signal with a process input and inputs the comparison signal to the microcomputer, and a sampling holding circuit that holds the output signal of the current-voltage conversion circuit under the control of the microcomputer. A digital arithmetic device.