JPH0219882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process converter that converts signals corresponding to various process quantities such as flow rate, pressure, and tension into predetermined output signals. This invention relates to an improvement in a process converter that can change the conversion characteristics between.

Figure 1 is a circuit diagram showing a two-wire converter as a conventional method, in which power from a receiving section, etc. is applied between line terminals L ₁ and L ₂ via a two-wire line. is stabilized by a constant voltage diode ZD and is used as the power supply voltage for the differential amplifier A side.

In addition, as the sensor S, two variable impedances etc. connected in series are used, and after applying a power supply voltage to these, a voltage is applied according to the impedance value of both variable impedances, which changes depending on the process amount to be detected. is extracted from both variable impedance connection points and used as a signal corresponding to the process amount.

The signal corresponding to this process amount is connected to the input resistor.
The voltage is applied to the non-inverting input of differential amplifier A as a conversion circuit via R ₁ , while the divided voltage of the voltage divider consisting of resistors R ₂ to _{R 6} is applied to the inverting input of differential amplifier A, which is connected to the strap terminal. The voltage taken out by the strap between t ₁ - t ₄ and t ₅ , t ₆ and set by the potentiometer RV ₁ is applied to the input resistor R ₇
is given as a reference voltage via the sensor S
After amplifying the voltage from the differential amplifier A as a differential voltage between both inputs, the FET (Field Effect Transistor.) Q inserted between the line terminals L ₁ and L ₂ is controlled.
The current value of the line current flowing between the line terminals L ₁ and L ₂ is determined as the output signal.

However, the inverting input of differential amplifier A is connected to a resistor.
It is connected to the reference potential COM via _R8 , but the non-inverting input has a feedback resistor through which the line current flows.
The terminal voltage generated at _R9 is divided by a voltage divider consisting of resistors _R10 to _R12 , and then applied to the strap terminals T7 to _T7 .
The voltage obtained by setting the potentiometer RV ₂ through the straps t ₁₀ , t ₁₁ , and t ₁₂ is applied as a negative feedback voltage through the resistor R ₁₃ . Efforts are being made to stabilize the line current.

The line current between line terminals L ₁ and L ₂ is a unified signal with a variation range of 4 to 20 mA, which is specified in the field of industrial measurement. Adjustment of the strap and potentiometer RV ₂ between the strap terminals t ₇ - t ₁₀ and t ₁₁ , t ₁₂ is used to determine the conversion gain between the change in the signal and the change in the line current. To determine the reference value of 4 mA in this example, connect strap terminals t ₁ to _{t 4} and
Strap and potentiometer with t ₅ , t ₆
RV ₁ adjustment is to be used.

Therefore, the setting of the span that defines the detection range of the process quantity according to the change range of the line current is performed by the span setting section SS using the resistors R ₁₀ to R ₁₂ and the potentiometer RV ₂ . , line current reference value setting is done by resistor R ₂
This is done by the reference value setting section FS using ~R ₆ and potentiometer RV _1. For example, if the reference value variable range is set to ±100% and the span is set to 1,
Each constant is selected with the intention of selecting 0.1, 0.01, etc.

Here, if we change the span from 1 to 0.01, the reference value variable range will be from ±100% to ±10000%.
Therefore, when the span is changed, the reference value setting section FS also needs to be changed.

For this reason, in the configuration shown in FIG. 1, the straps must be changed simultaneously in the reference value setting section FS and the span setting section SS, resulting in a drawback that these operations are troublesome.

The present invention has the purpose of eliminating such drawbacks of the conventional technology at once, and provides an extremely effective process converter that can simultaneously set the reference value variable range and the span variable range by switching operation of one circuit. It provides:

The details of the present invention will be explained below with reference to FIG. 2 and subsequent figures showing embodiments.

In the circuit diagram of FIG. 2, the output of the sensor S is applied to the inverting input of the differential amplifier A, while the voltage that determines the reference value from the potentiometer RV ₁ and the terminal voltage of the feedback resistor R ₉ are The negative feedback voltage taken out by resistor R ₂₀ and potentiometer RV ₂ is added by an adder consisting of resistors R ₂₁ to _{R 23} and then applied to the non-inverting input of differential amplifier A.
Potentiometer RV ₁ is used to vary the reference value, and potentiometer RV ₂ is used to vary the span, that is, the conversion gain. The strap between ₂₁ to _t23 and _t24 is variable by performing a bypass impedance circuit selection consisting of resistors _R24 to _R29 .

Figure 3 shows an equivalent circuit centered on the adder,
The resistance values of resistors R ₂₁ to R ₂₃ are R, the resistance values of potentiometers RV ₁ and RV ₂ are r, respectively.
Let the parallel resistance values of R ₂₄ , R ₂₅ , _and R 27, and R ₂₈ and R ₂₉ be R, R/2, and R/4, respectively, and select each constant so that they have the relationship R≫r. , the ratio between the input voltage Ei and the reference voltage E ₁ of the differential amplifier A, and the ratio between the input voltage Ei and the feedback voltage E ₂ are equal to each other. Next, this point will be explained in detail.

First, when the strap terminal _t24 is open, the feedback voltage is
The voltage division ratio of the resistor network when looking at the non-inverting input terminal (10) of differential amplifier A from the reference voltage E ₁ when E ₂ is set to zero, and the feedback when the reference voltage E ₁ is set to zero. The voltage dividing ratio of the resistor network when looking at the non-inverting input terminal (10) of the differential amplifier A from the voltage _E2 is as follows, since the resistor network is symmetrical due to the selection of constants described above. Equal.

Therefore, when E ₂ is set to zero, the signal voltage Ei with respect to the reference voltage E ₁ is determined by selecting the constant as described above and further considering R≫r, Ei = (R/2) E ₁ / [R + ( R/2)] = 1/3 = K ₁ ...(1). Similarly, when E ₁ is set to zero, the signal voltage Ei with respect to the reference voltage E ₂ is also expressed by the same equation as equation (1). In other words, we obtain the following relationship: Ei/E ₁ = Ei/E ₂ = K ₁ (2).

Next, if you connect strap terminals t ₂₁ and t ₂₄ ,
Similarly, Ei/E ₁ =Ei/E ₂ =(R/3)E ₁ /[R+(R/3)] =1/4=K ₂ (3).

Similarly, if strap terminals t ₂₂ and t ₂₄ and t ₂₃ and t ₂₄ are connected, Ei/E ₁ = Ei/E ₂ = (R/4) E ₁ / [R+(R/4)] = 1/5] K ₃ ...(4) Ei/E ₁ = Ei/E ₂ = (R/6) E ₁ / [R+(R/6)] = 1/7 = K ₄ ... (5).

As described above, the conversion gain variable range and the reference value variable range can be simultaneously set in a constant relationship.

In addition, since it is necessary to maintain the DC voltage at the non-inverting input of the differential amplifier A to approximately 1/2 of the power supply voltage, the resistors R ₂₄ and R ₂₅ , R ₂₆ and R ₂₇ , R ₂₈ and R in FIG. ₂₉ and 29 have the same resistance value, and to simplify this, as shown in Figure 4, the resistors
Only R ₂₈ and R ₂₉ are provided, and a variable resistor RV ₃ is inserted between these connection points and the non-inverting input of differential amplifier A, and the bypass impedance can be varied by adjusting variable resistor RV ₃ . The same goes for getting old. Yes,
Depending on the conditions, a single variable resistor may be inserted between the non-inverting input of the differential amplifier A and the reference potential COM.

In addition, depending on the type of sensor S, a circuit with a corresponding configuration may be inserted into the output side of sensor S, and a conversion circuit after differential amplifier A may be selected depending on the output signal condition. Various modifications are possible.

As is clear from the above explanation, according to the present invention, the conversion gain of the output signal and the reference value variable range can be set simultaneously by switching one circuit, so the adjustment man-hours are halved compared to the conventional method, and it can be used for various processes. Great benefits can be obtained in the transducer.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is an equivalent circuit centered on the adder in Fig. 2, and Fig. 4 is another embodiment. FIG. S...Sensor, _RV1 , _RV2 ...Potentiometer, _R9 ...Feedback resistor, _R20 to _R29 ...Resistor,
A...Differential amplifier (conversion circuit), _t21 to _t24 ...Strap terminals.

Claims (1)

[Claims] 1 In a process converter equipped with a conversion circuit that converts a signal corresponding to a process amount into a predetermined output signal, a feedback voltage corresponding to the output signal relative to a reference potential point and a reference voltage relative to the reference potential point are divided. voltage dividing circuit means for dividing a voltage defining a reference value of the output signal at the same voltage division ratio and outputting the divided voltage as an input signal to the conversion circuit; and an input terminal of the conversion circuit to which the input signal is input; and a variable means for changing the voltage division ratio by varying the impedance between the reference potential point and the conversion gain between the signal corresponding to the process amount and the output signal and the conversion gain in the output signal. A converter for a process, characterized in that a variable range of a reference value is set at the same time by the variable means.