JPH0138719Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a frequency signal transmission device. More specifically, the present invention relates to a device that converts an input analog signal into a frequency signal on a transmitting side and transmits the converted frequency signal, and measures the frequency signal on a receiving side to obtain a digitized signal.

As a conventional example of this type of device, the one shown in FIG. 1 is common. i.e. input analog signal
Ex is converted into a frequency x by a V/f converter consisting of an integrator I, a comparator COMP, and a switching circuit SW, and is transmitted to the receiving side through a transmission line. At this time, the frequency x is given by the following equation.

x=1/CR・Ex/Er (1) where CR is the time constant of integration and Er is the reference value for comparison. This frequency x is repeatedly measured by a counter CUNT. The counter CUNT repeats the operation of measuring for a time determined by the reference clock frequency s and the scale factor M and displaying the measured value obtained during that time. Therefore, the measured value N displayed by the counter CUNT is given by the following equation, and a digital signal proportional to the analog signal Ex is obtained.

N=x/s・M (2) =Ex・1/CR・1/Er・M/s (3) As is clear from equation (3), the measured value N is the integral time constant
Affected by CR. Therefore, stable C and R must be used, but it is not easy to obtain C with a small temperature coefficient. The oscillator for the reference clock frequency s also needs to be highly stable.

It is an object of the present invention to provide a simple frequency signal transmission device that is not affected by the integration time constant of the V/f converter and does not require a highly stable reference clock oscillator.

In this invention, the V/f converter on the transmitting side alternately converts the input analog signal and the reference analog signal into frequencies and transmits them, and the receiving side converts the controllable oscillator to the frequency corresponding to the reference analog signal. This frequency is used as a reference clock frequency to control the measurement operation of the counter.

The present invention will be explained below with reference to the drawings. FIG. 2 is a conceptual block diagram of an embodiment of the present invention. In Figure 2, VFC is the same V/f converter as in Figure 1, C and R are the capacitor and resistor that determine the integration time constant, respectively, Ex is the input analog signal source,
Ek is a reference analog signal source, and S is a changeover switch. These are installed on the sending side. The changeover switch S performs switching operation at a constant cycle (drive circuit omitted), and input analog signal Ex and reference analog signal
Ek is alternately input to the V/f converter VFC. This allows the V/f converter VFC to convert the input analog signal
Ex and reference analog signal Ek are alternately converted to frequencies x and k and transmitted. These frequencies x and k are respectively expressed by the following equations.

x=1/CR・Ex/Er (4) k=1/CR・Ek/Er (5) CUNT is the same counter as in Figure 1,
VCO is a controllable oscillator, S&H is a sample and hold circuit, FCM is a frequency comparator, and FDT is a frequency detector. These are installed on the receiving side. The counter CUNT is controlled to measure x of the transmitted frequencies. The measurement time is determined by the frequency of the output signal of the controllable oscillator VCO and the scale factor M. The controllable oscillator VCO oscillates under the control of the output of the sample and hold circuit S&H. The sample and hold circuit S&H samples and holds the output of the frequency comparator FCM when frequency k is being transmitted, according to the output of the frequency detector FDT. Since the frequency comparator FCM generates a control output according to the difference between the frequency of the controllable oscillator VCO and the transmission frequency, the controllable oscillator VCO will oscillate at the frequency k. Therefore, the measured value obtained by the counter CUNT is N=x/k・M=(1/CR・Ex/Er/1/CR・Ek/Er)M=Ex/Er・M (6). As is clear from equation (6), the measured value N does not include the term of the integral time constant. Digital measurement values that are not affected by the integration time constant are thus obtained. Note that although the measured value N is influenced by the reference analog signal Ek, it is easy to stabilize the reference analog signal Ek. Further, since the scale factor M is a fixed value preset in the counter CUNT, no fluctuation occurs. The reference clock that defines the measurement time of the counter CUNT is the controllable oscillator VCO.
However, since the controllable oscillator VCO is periodically regulated by the frequency k transmitted from the transmitter, it only needs to be stable for a short period of time, and is not as stable as the oscillator in conventional devices. is not required. If the input amplifier of the V/f converter VFC has an offset, etc., the signal Eo corresponding to the zero signal is converted to o and the receiving side calculates N = (x-o/k
-o) M may also be used.

If the part consisting of the input analog signal source Ex, reference analog signal source Ek, and changeover switch S in Figure 2 is replaced with the circuit in Figure 3, the partial pressure ratio (displacement amount of the slide) α of the potentiometer P can be digitally measured. can do. That is, N=(1/CR・αEk/Er/1/CR・Ek/Er)M (7) =αM (8). This field is also no longer affected by fluctuations in the reference analog signal Ek.

The above is an example in which a voltage is used as an input signal, but a capacitor or a resistor can also be used as an input signal. In that case, a single analog signal source is provided, and two capacitors C or resistors R are provided, one on the variable side and the other on the reference side, for determining the integration time constant, and these are periodically switched. Then, for example, the capacitor Cx on the variable side
When changes in inverse proportion to the displacement input X, a digital measurement value proportional to the displacement X is obtained as follows.

N=1/k/x・R・Ek/Er/1/k/xo・R・Ek/ErM (9) =x/xo・M (10) Another embodiment of the present invention is shown in FIG. . In Fig. 4, VFC is a V/f converter, which is configured by combining a current/frequency converter I/f, a voltage/current converter V/I, a reference voltage source Er, an output transistor To, and its driver. Ru. Such a V/f converter VFC is commercially available as an LSI. A power supply voltage is applied to the V/f converter VFC from the receiving side through a transmission line. This transmission line is also used for transmitting frequency signals. On the receiving side, TR is a receiving transistor, CUNT is a counter similar to that shown in FIG. 2, and CKT is a preceding circuit similar to that shown in FIG.

The V/f converter VFC alternately transmits frequencies x and k to the receiving side by an operation similar to that of the device shown in FIG. The receiving transistor TR performs an on/off operation according to the received frequency, and provides an output signal accordingly to the circuit CKT. Then, by the same operation as described above of the circuit CKT and the counter CUNT, a digital signal proportional to the input analog signal Ex is obtained at the counter CUNT. This device is a so-called two-wire signal transmission device in which the operating power supply path for the transmitting circuit and the frequency signal transmission path are shared.

The frequency signal may be transmitted wirelessly.

As described above, according to the present invention, a frequency transmission device with a simple configuration that is not affected by the integration time constant of the V/f converter can be obtained. Additionally, the device of the present invention does not require a highly stable oscillator to generate the reference clock signal, so it can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is an electrical configuration diagram of a conventional example, FIG. 2 is an electrical configuration diagram of an embodiment of the present invention, FIG. 3 is a partial modification of the device shown in FIG. FIG. 3 is an electrical configuration diagram of an embodiment. VFC...V/f converter, S...changeover switch,
FDT...Frequency detector, FCM...Frequency comparator, S&H...Sample and hold circuit, VCO...
...Controllable oscillator, CUNT...Counter.

Claims (1)

[Claims for Utility Model Registration] An analog signal/frequency converter disposed on the transmitting side that receives an input analog signal and a reference analog signal alternately and converts these analog signals into frequency signals, and a receiving side. a frequency detector disposed in the analog signal/frequency converter for detecting the frequency signal transmitted from the analog signal/frequency converter; and a frequency detector arranged to detect the frequency signal transmitted from the analog signal/frequency converter; a frequency comparator that generates a control signal based on a difference between input signals; and an output of the frequency comparator when the frequency detector detects a frequency signal obtained by converting a reference analog signal transmitted from an analog signal/frequency converter. A sample and hold circuit that samples and holds the signal,
By determining the measurement time of the counter by the output of the controllable oscillator that oscillates under the control of the output of the sample-and-hold circuit, a frequency signal obtained by converting the input analog signal transmitted from the analog signal/frequency converter is generated. A frequency signal transmission device comprising: a counter controlled to measure; and a frequency signal transmission device.