JPS6315611B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog signal input device using a microcomputer (hereinafter abbreviated as μCPU).

In recent years, with the advancement of μCPUs, there are increasing opportunities to incorporate μCPUs into various measurement and control devices to perform data processing, etc. In process measurement equipment, the relationship between analog signals representing various process quantities, the measurement equipment itself, and multiple analog signals is as follows:
The signals must be isolated from each other. For example, in a sewage treatment plant, the sludge concentration at points A and B is measured, and the calculation results of these two amounts are used to control the pump.
For measurement control equipment that turns on and off,
It is common for the ground potentials at points A and B to be different. At this time, unless signal isolation is provided between each signal, each measured value will be affected by the wraparound of the signals.
It cannot be accurate and may cause malfunction. Furthermore, when applying the μCPU to measurement control equipment, an analog-to-digital conversion circuit is required to input analog signals from various processes into the μCPU. The method for converting analog signals into digital signals while providing signal isolation in this process is as follows:
The following three methods are possible.

Analog signal isolation circuit + A/D conversion circuit A/D conversion circuit + digital signal isolator V/F conversion circuit + digital signal isolator + counting circuit Generally, the method widely used is the method . Both methods have fast conversion times, but have complex circuit configurations.
It has drawbacks such as being expensive. The method is small,
Although it is low cost and has a simple circuit configuration, a certain gate time is required to count the frequency output proportional to the input signal, and to achieve the same level of accuracy as the method of , the conversion time is 100 ~ There is a drawback that it costs 1000 times more. The measuring instruments to which this method can be applied are limited to those in which the process amount does not change suddenly, such as in sewerage processes.

The present invention has been made in view of the above circumstances, and its purpose is to convert analog signals from various processes into digital signals while insulating the signals. This provides an input device for the following.

Hereinafter, the present invention will be explained in detail based on FIGS. 1 and 2.

In FIG. 1, 1 is a preamplifier that increases the input impedance. Voltage-frequency conversion circuit (hereinafter abbreviated as V/F conversion circuit) described below
The reason why the positive phase input of the second integrator 21 is set to -1V is to prevent the time t from becoming infinite and making the interval timer measurement impossible when the input voltage Vin is zero. V/F conversion circuit 2 is an integrator 2
1, a comparator 22, a one shot 23, and a constant current source 24. This V/F conversion circuit 2
When the input Vc of the comparator 22 is less than 0, the one shot 23 is operated, the output ₀ becomes "H", and the switch SW1 is turned on. At this time,
The capacitor C1 starts charging, and the charging speed is determined by the integrator 21 as dv/dt=(Ic-Vin/
R1)/C1. The capacitor C1 continues to charge only during the one-shot time T, and after the time T, the output ₀ becomes "L" and the switch SW1 is turned OFF. At this time, the comparator input Vc is Vc=dv/
dt·T=(Ic−Vin/R1)T/C1. When switch SW1 turns OFF, capacitor C1 becomes dv/dt.
Discharge begins with a slope of =-Vin/R1C1. If the input Vc of the comparator 22 continues to discharge and becomes zero, the one shot will work again and the output will be _0.
becomes “H” and at the same time switch SW1 is turned ON. Repeating this operation, the output ₀ becomes ″
Repeat H" and "L". If the time required for discharging is t, the charge charged during T is equal to the charge discharged during t, so (Ic-Vin/R1)T/ C1=Vin/R1C1・t Vin=IcT/C1・R1C1/T+t Therefore, since 1/(T+t)=out, Vin∝out is obtained, and a frequency output proportional to the input voltage is obtained.

4 is an interval timer, and V/F conversion circuit 2
input the signal from V/ through the signal isolator 3.
The time of the "L" signal output from the F conversion circuit 2 is measured and output to the μCPU 5. The μCPU 5 performs calculations based on the time t input from the interval timer 4 to obtain an analog input value.

Figure 2 shows the voltage input to the comparator 22.
3 is a graph diagram showing the relationship between Vc and the output ₀ from the one shot 23. FIG.

The operation of the device configured as described above will be explained next.

Now, the analog signal Vin is input to the preamplifier 1, amplified, and outputted to the comparator 22 as Vc via the integrator 21. The comparator 22 outputs a signal to the one shot 23 when Vc becomes less than zero, as shown at time _{t 0 in} A in FIG. The ``H'' signal is output to the interval timer 4 via the signal isolator 3, and the switch SW
Turn on 1. The signal from the one shot 23 is output as an "H" signal for a time T from time _t0 to time _t1 . During this time T, capacitor C1 is charged. At time t ₁ , the one shot 23 outputs the "L" signal, and the switch SW
Turn 1 off. By turning off the switch SW1, the capacitor C1 is discharged for a time t from time _t1 to time _t2 . When the capacitor C1 is discharged and Vc becomes as shown at time _t2 , the comparator 22 outputs a signal to the one shot 23, and the one shot 23 outputs an "H" signal. In this way, in the V/F conversion circuit 2,
The signal isolator 3 outputs the H″ and “L” signals.
input to interval timer 4 via
Measure the time of the L″ signal and output it to μCPU5.
The μCPU calculates Vin=RiIc・T/T+t (1) to obtain the analog input value.

At this time, the reference clock of interval timer 4 is
If it is 10 MHz or more and the output _{is 0} = 10 KHz, the accuracy when measuring t is 10 KHz/10 MHz = 1/1000. Also, when the gain of the integrated amplifier 1 is doubled, the μCPU 5 calculates it using the following formula: V=1/2(K/T+t-1)...(2). K is a constant of V/F conversion circuit 2,
For example, K=10V/10KHz=0.001 (V/Hz).

This equation (2) expresses the output of integrated amplifier 1 as V ₀
Then, V ₀ = G・Vin ...(3) V ₀ +1=K・₀ = K/T+t ...(4), and from equations (3) and (4), Vin=1/G(K/T+t- 1) is obtained.

As described above, the present invention includes a preamplifier 1, a V/F conversion circuit 2, a signal isolator 3, and an interval timer 4 in order to input an analog signal from a process.
By inputting to μCPU5 via
Since the output from the conversion circuit 2 is only a frequency signal, signal isolation is easy, and conventionally, V/
The signal from the F conversion circuit 2 can be inputted in an extremely short time compared to counting the signal with a frequency counter. for example
If a resolution of 1/1000 is required when reading a 10KHz frequency output, the gate time of a conventional frequency counter is 1/10KHz x 1000 = 100msec.
However, in the present invention, due to the accuracy of the timer that measures t, it can be read in 1/10 KHz=100 μsec, and the conversion speed is 1000 times faster. Furthermore, since the circuit configuration is simple, it has excellent advantages such as being able to realize small size and low cost in terms of hardware.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and FIG. 2 is a graph diagram for explaining the present invention. 1 is a preamplifier, 2 is a V/F conversion circuit, 21 is an integrator, 22 is a comparator, 23 is a one shot, 24 is a constant current source, 3 is a signal isolator, 4 is an interval timer, and 5 is a μCPU.

Claims (1)

[Claims] 1. When inputting analog signals to a microcomputer using a voltage-frequency conversion circuit,
The signal is introduced into a voltage-frequency conversion circuit having an integrator that integrates the analog signal, and a pulse generator that outputs a one-shot pulse according to the output state of the integrator, and the signal from the voltage-frequency conversion circuit. is input through a signal isolator, and an interval timer that measures the time between pulses of consecutive frequency signals is input. The measured value of this interval timer is input, and calculations are performed based on this measured value. An analog signal input device comprising: the microcomputer for calculating a value.