JPS6335384Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a thermocouple input temperature measuring device using a millivolt isolator.

The temperature measuring device of the present invention is equipped with a compensation means for compensating for gain fluctuations of the millivolt isolator due to temperature changes. Here, the millivolt isolator has already been proposed in the patent application filed in 1972 by the applicant of the present application.
This is proposed as No. 107511. below,
Before explaining the present invention, a millivolt isolator will be explained with reference to FIG.

In Figure 1, V _IN is the signal source under test, D,
D′ is a diode circuit constructed by connecting a pair of diodes in antiparallel. The characteristics of the current I with respect to the applied voltage V of both diode circuits are shown in FIG. T is a 1:1 pulse transformer with _a tertiary winding _n3 ;
Impulse current i ₀ shown in Figure A is supplied. C,
C' is a capacitor, and the input circuit is composed of the capacitor C, the diode circuit D, and the primary winding _n1 of the transformer T, and the input circuit is composed of the secondary winding _n2 of the transformer T, the diode circuit D', and the capacitor C'. An output circuit is configured. If transformer T is an ideal transformer, the voltage generated in the primary and secondary windings n ₁ and n ₂ of transformer T is
For currents i ₁ and i ₂ flowing through e ₁ and e 2 and windings n ₁ and n _{2 ,} e ₁ =
If the relationship e ₂ , i ₁ +i ₂ =i ₀ holds true, and further considering the left-right symmetry seen from the transformer T, then i ₁ =i ₂ =i ₀ /2 in the steady state. If the impulse current i ₀ supplied to the tertiary winding n ₃ is a current with an amplitude of ±1 ₀ shown in Figure 2 A, then i ₁ and i ₂ are pulses with an amplitude of ±I ₀ /2 as shown in Figure 3 B. It becomes an electric current.

In the V, I characteristics of diodes D and D' shown in Fig. 2, the absolute values of the voltages between the terminals corresponding to I = ±I ₀ /2 are Δ ₁ , Δ ₂ (for D', Δ' ₁ , Δ′ ₂ ), the voltage e ₁ generated in the primary winding n ₁ of the transformer T becomes (V _IN +Δ ₁ ) when the impulse current i ₀ is a positive pulse.
When i ₀ is a negative pulse, it becomes (V _IN +Δ ₂ ). Similarly, the voltage e ₂ of the winding n ₂ of the output circuit is e 2 = V _OUT + Δ′ ₁ when i ₀ is a positive pulse, and e ₂ = V OUT − Δ when it is a negative pulse, as shown _{in Figure 3} C. ′ ₂ . Voltage e ₂ is filtered by capacitor C ₂ resulting in an output voltage V _OUT . This output voltage E ₂ is balanced at a value that satisfies e ₁ =e ₂ .
In other words, the output voltage V _OUT is expressed as: When i ₀ is a positive pulse, ... V _IN + Δ ₁ = V _OUT + Δ' ₁ When i ₀ is a negative pulse, ... V _IN − Δ ₂ = V _OUT − Δ' ₂ It is derived as the average value of the two equations.

V _OUT =V _IN −Δ ₁ −Δ′ ₁ /2−Δ ₂ −Δ′ ₂ /2 …(1) Therefore, if Δ ₁ = Δ′ ₁ and Δ ₂ = Δ′ ₂ ,
V _OUT is equal to the input DC voltage V _IN and is electrically isolated from the input circuit.

By the way, in such a millivolt isolator, if a pulse transformer T with an inductance temperature coefficient close to zero is used, the influence of the temperature coefficient due to temperature changes in the diodes V _BE used in the diode circuits D and D' will affect the input and output. This appears with respect to the gain (almost 1:1) of the transfer characteristic between.
The temperature coefficient value of V _BE is approximately -100±30ppm/°C. Therefore, in the temperature measuring device using the millivolt isolator shown in FIG. 1, correct accuracy with respect to ambient temperature changes cannot be obtained unless the temperature coefficient is corrected.

In the present invention, when a millivolt isolator is used as a thermocouple input temperature measuring device, a temperature detection circuit for compensating the reference junction of the thermocouple is used to compensate for the temperature of the millivolt isolator.

FIG. 4 is a block diagram of an embodiment of a thermocouple input temperature measuring device according to the present invention. In FIG. 4, 1 is the millivolt isolator shown in FIG. 1, 2 is a temperature detection circuit for reference junction compensation, 3 is a double-throw changeover switch, 4 is an analog-to-digital converter, 5 is a microprocessor, and 6 is a A display or printer 7 for displaying or printing the output of the microprocessor 5 is a thermocouple.

A thermocouple 7 is connected to the input of the millivolt isolator 1. The output terminals of the millivolt isolator 1 and the reference junction compensation temperature detection circuit 2 are connected to an analog-to-digital converter 4 via a changeover switch 3.
The output of the analog/digital converter 4 is connected to a display or printer 6 via a microprocessor 5.

In such a configuration, the thermoelectromotive force of the thermocouple 7
By inputting V _IN to the millivolt isolator 7, an output voltage V _OUT which is equal to V IN and electrically isolated is taken out from the output terminal of this isolator, as expressed _by equation (1). on the other hand,
The reference junction compensation temperature detection circuit 2 outputs a voltage corresponding to room temperature.

Here, if the gain of millivolt isolator 1 at a certain reference temperature T ₀ is G ₀ , then the gain G of millivolt isolator 1 at room temperature T
When the temperature coefficient is α (-100±30ppm/℃), G=G ₀ (1+αΔT)...(2) However, it is expressed as ΔT=T−T ₀ . When adjusting the millivolt isolator 1 at the manufacturing stage, the reference temperature T ₀ ,
The values of the gain G ₀ and the temperature coefficient α are stored in the ROM of the microprocessor 5 in advance.

When actually measuring the temperature, the output of the reference junction compensation temperature detection circuit 2 is switched to the switch 3.
The signal is taken out by the analog/digital converter 4, converted into a digital signal, and inputted to the microprocessor 5. The microprocessor 5 obtains the room temperature _T1 based on the input. Next, switch 3 switches the output of millivolt isolator 1 to analog
Convert it into a digital signal with a digital converter 4,
The digital signal is input to the microprocessor 5. The microprocessor 5 calculates the voltage corresponding to the room temperature T ₁ output by the reference junction compensation temperature detection circuit 2 and the gain G ₀ of the millivolt isolator 1 at the reference temperature T ₀ already stored in the ROM of the microprocessor 5. From the temperature coefficient α, calculate G ₁ = G ₀ (1 + αΔT ₁ ) …(3) ΔT ₁ = T ₁ − T ₀ , and calculate the gain at room temperature T ₁ .
Get _G1 . Therefore, the gain G ₁ of millivolt isolator 1 is temperature compensated and the gain G 1 of millivolt isolator 1 is
Data with compensated temperature coefficients is obtained. This output is displayed on a print or display circuit 7. Since the temperature coefficient α has a range of α=100±30ppm,
Maximum when corrected at α=-100ppm/℃
Although the temperature coefficient change of 30ppm/℃ will remain,
If this is also to be compensated for, the temperature coefficient α may also be measured in advance and the microprocessor 5 may memorize the accurate value α. In addition, thermocouple 8
The reference junction temperature can be easily compensated for by subtracting the output of the reference junction compensation temperature detection circuit 2 from the output of the thermocouple 8 in the microprocessor 5.

As described above, according to the present invention, it is possible to measure the temperature of a thermocouple input using a millivolt isolator without being affected by changes in ambient temperature.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a millivolt isolator used in the present invention, Figures 2 and 3 are diagrams for explaining the operation of the circuit in Figure 1, and Figure 4 is a circuit diagram of an embodiment of the present invention. be. 1...millivolt isolator, 2...temperature detection circuit for reference junction compensation, 3...switch, 4...
Analog-digital converter, 5... microprocessor, 6... display or printer, 7... thermocouple.

Claims (1)

[Claims for Utility Model Registration] A pulse transformer having primary, secondary, and tertiary windings, two sets of diode circuits each having a pair of diodes connected in antiparallel, and a pair of capacitors; An input circuit is constructed by connecting one set of anti-parallel connected diode circuits in series to the winding and connecting one of the capacitors in parallel, and the other set of anti-parallel connected diode circuits is connected to the secondary winding. A millivolt isolator is connected in series and another capacitor is connected in parallel to form an output circuit to give a pulse signal to the tertiary winding provided in the transformer. a temperature detection circuit for reference junction compensation that detects room temperature _T1 and outputs power corresponding to this room temperature, and an analog-to-digital conversion that converts the outputs of the millivolt isolator and the temperature detection circuit for reference junction compensation into digital signals. Based on the gain G ₀ of the millivolt isolator at a certain reference temperature T ₀ , the temperature coefficient α of the millivolt isolator, and the output of the reference junction compensation temperature detection circuit corresponding to the room temperature T ₁ , the following formula is calculated. _1. A temperature measuring device comprising: a microprocessor that performs the calculation shown in FIG. G ₁ =G ₀ (1+αΔT ₁ ) ΔT ₁ =T ₁ −T ₀