JPS647284Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of the invention] The present invention detects the temperature difference between the supply water and return water of an air conditioner, and detects the temperature difference used when measuring the amount of heat consumed in an air conditioning load. This invention relates to improvements in detection circuits.

[Prior art]

Conventionally, individual thermometers are used to detect the temperature difference between two points, and a two-wire or three-wire line is connected between the temperature sensor installed at the measurement point and the thermometer body. Although it is supposed to be connected,
In the two-wire system, the resistance of the line affects the measured value, so the wiring length between each measurement point and the thermometer body must be set equal, which makes installation work cumbersome. On the other hand, in the case of 3-wire system,
Although the influence of the resistance value of the line is smaller than that of the two-wire system, the same effect appears when the resistance value of the line increases due to an increase in the wiring length, so this method has the drawback that the wiring length cannot be increased. It is occurring.

[Summary of the invention]

The present invention has the purpose of eliminating such drawbacks of the conventional technology at once.
The same constant current is passed through the current wires to the first and second heat-sensitive elements, and the terminal voltage of each heat-sensitive element is derived from each individual voltage line. The terminal voltage of each heat-sensitive element is individually amplified through each voltage line, and the difference between the amplified outputs is determined by a subtraction circuit. The present invention provides an extremely effective temperature difference detection circuit in which the wiring length for each heat-sensitive element is irrelevant to the measured value.

[Example] Hereinafter, details of the present invention will be explained with reference to circuit diagrams showing examples.

In the figure, first and second heat-sensitive elements TS ₁ and TS ₂ using a thermistor or the like whose resistance value changes depending on the temperature are housed in a probe or the like, and these are connected to the terminal board TB. are connected by first and second 4-core cables W ₁ and W ₂ , and cable W ₁ is connected to the first and second current wires.
L _i1 , L _i2 and the first and second voltage lines
The cable _{W 2} consists of third and fourth current lines L _i3 , L _i4 and third and fourth voltage lines L v3 , L v4 , and the cable W ₂ consists of third and fourth current lines L _i3 , L i4 and third and fourth voltage lines L v3 , L _v4 . _i1
One end of the voltage line L _v1 is directly connected to one terminal t ₁ of the thermal element TS ₁ , and one end of the current line L _i2 and voltage line L _v2 is connected directly to the other terminal t ₂ of the thermal element TS ₁ . In addition, one end of the current line L _i3 and the voltage line L _v3 is similarly connected to one terminal t ₃ of the heat sensitive element TS ₂ , and the current line L _i4 and the voltage line L _v4 are directly connected to each other. One end is similarly connected to the other terminal _t4 of the same element _TS2 .

In addition, the other ends of the current wires L _i2 and L _i3 are connected via the terminal plate TB by a short-circuit wire SL, and the constant current circuit I _s of the current wire L _i4 is connected, via which Power supply -V is applied and current line
A series resistor R _s is connected to the other end of L _i1 to bring the short circuit line SL to approximately zero volts, and a power supply +V having the same voltage as the power supply -V is applied through this resistor R s .

For this reason, each heat _- sensitive element _is
The same constant current passes through TS ₁ and TS ₂ , and the current line L _i1 ~
The constant current value becomes irrelevant to the resistance value of L _i4 ,
If heat-sensitive elements TS ₁ and TS ₂ having substantially the same characteristics are used, the voltages at these terminals will indicate the temperature at each measurement point.

In addition, since the power supplies +V and -V have the same voltage and opposite polarity, and a series resistor R _s is inserted, the short circuit line SL becomes almost 0V, which prevents leakage to each amplifier circuit described below. The current decreases significantly.

i.e. differential amplifier A ₁ and resistors R ₁ to _{R 4}
As a result, a first amplifier circuit having high input impedance is configured, and a differential amplifier A ₂
A similar second amplifier circuit is configured by resistors R ₅ to R ₈ , and voltage lines L _v1 ,
Since the other ends of L _v2 , L _v3 , and L _v4 are connected via the terminal plate TB, the terminal voltages between terminals t ₁ and t ₂ and between t ₃ and t ₄ are each amplified by the same amplification degree. .

Each output of each amplifier circuit is given as an input to a subtraction circuit constituted by a differential amplifier A ₃ , resistors R ₉ to R ₁₄ and potentiometers RV ₁ and RV ₂ ,
A voltage corresponding to the difference between each output is sent to the output OUT, which indicates the temperature difference between each measurement point detected by each heat-sensitive element TS ₁ , TS ₂ .

Therefore, the temperature difference between each measurement point can be detected with a simple configuration, and the negative feedback provided by the resistors R ₄ and R ₈ allows each DC amplification circuit made up of the differential amplifiers A ₁ and A ₂ to have a high input impedance. Therefore, no current flows through the current wires L _v1 to _{L v4} , and their resistance values are completely unrelated to _the measured _value . _2. Regardless of the wiring length, you can always obtain an accurate temperature difference.

Note that a bias voltage is applied to the non-inverting input of the differential amplifier A ₃ from the potentiometer RV ₂ via the resistors R ₁₁ and R ₁₃ .
By setting RV, the zero point adjustment of the output OUT is performed, while the negative feedback to the movable element of the potentiometer RV ₁ inserted between the output of the differential amplifier A ₃ and the common circuit is performed. A resistor _R14 is connected, and the amplification degree is adjusted by setting the potentiometer _RV1 , and the span of the output OUT is adjusted.

In addition, if the core wires in the cables W ₁ and W ₂ are paired wires such as twisted wires, noise components due to electromagnetic induction are canceled out, and the measurement situation becomes stable.

However, depending on the situation, each line L _i1 ~ L _i4 , L _v1 ~
L _v4 may be individually wired, and other configurations may be applied to each amplifier circuit and subtraction circuit as long as they exhibit equivalent functions, and various modifications are possible.

[Effect of idea]

As is clear from the above explanation, the length of the wiring to each heat-sensitive element is irrelevant to the measured value, and if you select one with characteristics similar to each heat-sensitive element, there is no need to make adjustments according to the length of the wire. , the circuit configuration is simplified, the manufacturing cost can be easily reduced, the wiring length can be freely selected, the installation work is simplified, and a great effect can be obtained in detecting temperature differences in various applications.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the present invention. TS ₁ , TS ₂ ...thermal element, t ₁ - _{t 4} ... terminal, L _i1 - _{L i4}
…Current line, L _v1 to _{L v4} …Voltage line, SL…Short line, Is…
Constant current circuit, Rs...series resistor, _A1 to _A3 ...differential amplifier, _R1 to _R14 ...resistor.

Claims (1)

[Scope of utility model registration request] The first and second resistance values change depending on the temperature.
a first current line and a first voltage line, one end of which is connected to one terminal of the first thermal element, and a first voltage line, one end of which is connected to the other terminal of the first thermal element. a third current line and a third voltage line, one end of which is connected to one terminal of the second heat-sensitive element, and the other terminal of the second heat-sensitive element; a fourth current line and a fourth voltage line, one end of which is connected to the other end of the fourth current line, a short-circuit line that connects the other ends of the second and third current lines, and a short-circuit line that connects the other end of the fourth current line to the other end of the fourth current line; a constant current circuit that passes the same constant current to each of the heat-sensitive elements, a series resistor for bringing the potential of the short-circuit line to approximately zero V, and a connection to the other ends of the first and second voltage lines. a first amplification circuit connected to the other ends of the third and fourth voltage lines, and each output of the first and second amplification circuits as inputs; A temperature difference detection circuit comprising: a subtraction circuit that sends out an output according to the difference between the temperatures.