JPH0486015A - Active resistor - Google Patents

Abstract

PURPOSE:To set a value smaller than the resistance value of a current detection resistor by controlling a voltage to be applied to the current detection resistor through an amplifier. CONSTITUTION:An A/D converter 15 detects a voltage V0 related to a current I flowing to a current detection resistor 11 and applies the detected voltage to an arithmetic control part 16, and the arithmetic control part 16 calculates a voltage data Vx to be applied to a D/A converter 18 based on the value and outputs the calculated voltage data to the D/A converter 18. In this case, the arithmetic control part 16 detects the current I flowing to the current detection resistor 11 and controls the voltage Vx to be applied to the current detection resistor 11 through an amplifier 12 so as to obtain the desired resistance value set between output terminals 13 and 14. Thus, as the resistance value, a value smaller than a resistance value R0 of the current detection resistor 11 can be set.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active resistance device, and more particularly, to an active resistance device whose resistance value can be set from OΩ and which has no polarity.

(Prior art) For example, 211! Temperature measurement device using temperature resistance element! To calibrate, connect a variable resistor whose resistance value can be set arbitrarily instead of the resistance temperature detector to the resistance temperature detector connection terminal of the device, and set the resistance value of the variable resistor to the resistance of the resistance temperature detector. Temperature values are calibrated by changing them in response to changes in temperature.

Conventionally, variable resistors used in such calibration work include dial resistors, which are set to the desired resistance value by the operator rotating a dial, and multiple fixed resistors that are selectively switched and connected using relays. A resistor device or the like configured to set a desired resistance value is used.

However, with the former device, it is difficult to automate the calibration work, and with the latter device, although it is possible to automate the calibration work, it is difficult to obtain a highly accurate low resistance value, and relays are used. Therefore, there is a problem of poor responsiveness.

Therefore, it is conceivable to use an active resistance device that can set a desired resistance value using an electronic circuit, such as the one disclosed in Japanese Patent Publication No. 59-46128, for example.

FIG. 3 is a circuit diagram showing an example of an active resistance device disclosed in Japanese Patent Publication No. 59-46128. In FIG. 1, 1.2 is an equivalent resistance terminal, and terminal 1 is connected to the source of FET 3. and the amplifier 5 via the multiplier 4.
The terminal 2 is connected to the non-inverting input terminal of the terminal 2, and the terminal 2 is a common potential point. The drain of the FET 3 is connected to the common potential point via the reference resistor 6 and also to the inverting input terminal of the amplifier 5, and the gate is connected to the output terminal of the amplifier 5.

In such a configuration, if the voltage between terminals 1 and 2 is E, and the current flowing between terminals 1 and 2 is 1, then terminals 1 and 2
The equivalent resistance value R seen from the outside between the two is R=E/I
...(1). On the other hand, focusing on the input voltage of the amplifier 5, the output voltage E- of the multiplier 4 is applied to the non-inverting input terminal, and the 4S flowing to the reference resistor 6 is applied to the inverting input terminal. If the setting magnification of the 0 multiplier 4 to which the voltage drop due to the current I is added is X, the output voltage E- of the multiplier 4 is E-=B-X...(2
), and if the resistance value of the reference resistor 6 is RO, the voltage drop across the reference resistor 6 will be I-Ro. Here, assuming that the feedback amount of the amplifier 5 is sufficiently large, the FET
Since almost no ti flows to the gate of amplifier 5,
input; between pressures, I −Ro =E −X
- The relationship (3) holds true. Substituting these equations (2) and (3) into equation (1) to find the equivalent resistance value R, R=R,/X...(4
)become.

That is, by configuring as shown in FIG. 3, an active resistance device in which the equivalent resistance value R changes in inverse proportion to the set magnification X of the multiplier 4 can be realized.

(Problem to be solved by the invention) However, according to such a conventional configuration, the equivalent resistance value R
Since changes in inverse proportion to the set multiplier X of the multiplier,
This method has the disadvantage that the resistance value to be set is subject to division, which reduces the accuracy of setting the resistance value.

Another problem is that the desired resistance value cannot be made smaller than the resistance value (Ro) of the reference resistor 6 for detecting the t current.

Furthermore, since the circuit components have polarity, the active resistance device also has polarity, which may cause problems in use.

The present invention focuses on these points, and its purpose is to provide an active resistor device without polarity that allows resistance values to be set with high precision from OΩ! The goal is to offer.

(Means for Solving the Problems) The active resistance device of the present invention includes a t2X detection resistor, an A/D converter that converts the voltage generated across the t current detection resistor into a digital signal, and a desired A setting display section that sets and displays the resistance value of these AID changes! A calculation control unit that calculates the voltage data necessary to obtain the desired resistance value based on the output data of the device and set resistance value data and controls the entire system, and converts the voltage data calculated by the calculation control unit into an analog signal. A D/A converter that converts the D/A converter into a D/A converter and adds the D/A converter to the amplifier.

(Operation) The calculation side m section detects the current flowing through the current detection resistor and controls the voltage applied to the current detection resistor via the amplifier so that a desired resistance value set between the output terminals is obtained.

Thereby, it is possible to set and realize a desired resistance value that is smaller than the resistance value of the current detection resistor, and is not limited by polarity.

<Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In FIG. 1, one end of a current detection resistor 11 having a resistance value R0 is connected to the output terminal of an amplifier 12, and the other end is connected to a first output terminal 13. The amplifier 12 outputs a bipolar voltage, and a second output terminal 14 is also connected to the amplifier 12. An A/D converter 15 that converts the generated voltage into a digital signal is connected to both ends of the current detection resistor 11, and its output data is applied to an arithmetic control section 16. A setting display section 17 for setting and displaying a desired resistance value is connected to the calculation control section 16, and a D/A converter 18 is also connected thereto. The calculation control section 16 calculates voltage data necessary to obtain a desired resistance value based on the output data of the A/D converter 15 and the set resistance value data of the setting display section 17, and sends the data to the D/A converter 18. Output and overall control. Then, the D/'A converter 18 converts the voltage data applied from the arithmetic control section 16 into an analog signal and outputs it to the amplifier 12.

The operation of the thus refined device will now be described.

The voltage applied between terminals 13 and 14 is 2, and the current flowing in is 1. The voltage across the current detection resistor 11 is ■. , amplifier 1
If the output voltage of 2 is Vχ, then V=Vo+Vχ
...The relationship (5) is established, Vo= R,, -I ・(G
) holds true.

On the other hand, the resistance value you want to set, that is, the resistance value R seen from the outside, is R=V/I...(7
). From this formula (7), V=R・1...(8
), the output voltage of the amplifier 12, ■χ, becomes ■χ
=V-V0 R-I-RO・I =RO-1-1(R/RO) -1+ -(9)
By performing control so that the equation (7) holds true.

As is clear from equation (9), since the output voltage ■χ0 of the amplifier 12 may be negative, bipolar output types are used as the D/A converter 18 and the amplifier 12. Note that in order to make the I)/A converter 18 and the amplifier 12 bipolar in this manner, a known application circuit of a D, , , 'A converter may be used.

Specifically, the current detection resistor 1 is connected to the A//D converter 15.
1 detects the voltage v0 related to the current I flowing through D and adds it to the arithmetic controller 16, and the arithmetic controller 16 detects the voltage v0 related to the current I flowing through D
Since three steps are performed in which the voltage voltage given to the /A converter 18 is calculated and the calculated voltage data is output to the D7/A converter 18, if these three steps are considered as one cycle, D The voltage data ■χ inputted to the /A converter 18 is based on the current I- of one cycle before.

Therefore, formula (9) is ~'x = Ro-I - ((R/Ro) 1)
・・0■ Substituting this into equation (5), V=Vo +R
o HI −・I (R/Ro > 1) Ro
・(I−11+R−I−−−1111.Here, if 1−=1−Δ1...(12), equation (11) becomes ■=Ro ・ΔI+R,−(N−ΔI) -11
3) become.

As a result, 1= (V/R)+ (l-(RO/R)) ・ΔI・
...(14) becomes.

By refining in this way, it is possible to flow a current I that is proportional to the externally applied voltage and inversely proportional to the set resistance value R, or between the externally applied current I and the set resistance. A voltage proportional to iIR can be generated.

According to such refinement, the arithmetic control section 16
Detects current 1 flowing through current detection resistor 11 and outputs output terminal 1
3. Voltage ■ applied to the t current detection resistor 11 via the amplifier 12 so as to obtain the desired resistance value R# set between 3.14 and 14.
Since χ is controlled, the desired resistance value R can be set to a value smaller than the resistance value R6 of the current detection resistor 11, and the polarity is not limited.

(Effects of the Invention) As described above, according to the present invention, it is possible to realize an active resistance device without polarity whose resistance value can be set with high precision from 0Ω, and the practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional device.

Claims (1)

[Claims] A current detection resistor, an A/D converter that converts the voltage generated across the current detection resistor into a digital signal, a setting display section that sets and displays a desired resistance value, and these. A/
A calculation control unit that calculates voltage data necessary to obtain a desired resistance value based on the output data of the D converter and set resistance value data, and controls the entire system; An active resistance device comprising: a D/A converter that converts the signal into an analog signal and applies the signal to the amplifier.