JPS6120767B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermocircuit for a vaporization heater used in a combustor that vaporizes and burns liquid fuel such as petroleum, and particularly relates to a thermoelectromotive voltage amplification circuit when a thermocouple is used as a temperature sensor. This invention relates to a vaporization heater thermocircuit that simplifies the offset adjustment of an operational amplifier and the correction of the influence of the cold junction ambient temperature of a thermocouple.

Conventionally, for example, the temperature of the vaporization surface of an oil gasification combustor is important for oil gasification and must be detected accurately, and the temperature sensor of the vaporization heater thermocircuit has been designed to be able to withstand the high temperature environment. Thermocouples are commonly used, but because the temperature coefficient of thermoelectromotive voltage is small, they must be amplified, and operational amplifiers are used for this purpose.

However, the operational amplifier itself has problems such as offset voltage and current drift, and it has been necessary to adjust each operational amplifier to prevent these effects from affecting the electromotive voltage amplification of the thermocouple. It is also necessary to compensate for the zero point of the thermoelectromotive voltage of the thermocouple, and the voltage obtained by detecting the ambient temperature of the cold junction on the circuit side of the thermocouple with a thermistor, and the thermoelectromotive voltage amplified by the aforementioned operational amplifier. After inputting the voltage to the second-stage operational amplifier to obtain an output voltage that corrects the influence of the cold junction ambient temperature, a comparator can compare this output voltage with the voltage corresponding to the set temperature of the evaporative heater. A circuit configuration has been adopted in which the vaporization heater serving as a load is turned on and off based on the output signal.
Furthermore, even if the effects of the offset voltage and current of the second stage operational amplifier, temperature drift, etc. can be made relatively small in relation to the input voltage, the output voltage after cold junction ambient temperature correction is affected by variations in circuit constants, etc. It was necessary to make adjustments in order to turn the vaporization heater on and off at the set temperature.

In this way, in conventional thermo circuits of this type, adjustments are made separately to compensate for the operational amplifier's offset voltage and current, temperature drift, and the amplified output after compensating for the ambient temperature of the thermocouple's cold junction. Not only is adjustment complicated, but it also has many drawbacks, such as a large number of parts, increased production costs, and decreased reliability.

The present invention has been made to solve the above-mentioned drawbacks, and has a circuit configuration that allows compensation for the offset voltage and current of the operational amplifier, the influence of the ambient temperature of the cold junction of the thermocouple, etc., by making adjustments at one location. The purpose of the present invention is to provide a vaporization heater thermocircuit that is simple, has a small number of parts, and is highly reliable.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

Figure 1 shows the circuit of this embodiment. In the figure, 1 is a DC power supply, 2 is a thermocouple as a temperature sensor that detects the temperature of the vaporization surface, and A is a branch circuit, which is connected to the high potential side of the DC power supply 1. It consists of 3 to 7 resistors connected in series toward the low potential side, and 8 thermistors connected in parallel to the resistor 4 to detect the ambient temperature of the cold junction of the thermocouple 2. A semi-fixed resistor 9 is connected between the resistors 4 and 5 and between the resistors 6 and 7, and its movable terminal is connected to the + side of the cold junction of the thermocouple 2 (point a in the figure). B is an inverting amplification circuit, which is composed of 11 operational amplifiers having a power input line connected in parallel with branch circuit A and each resistor 12 to 14, and operational amplifier 11 is connected to the - side of thermocouple 2 (point b in the figure). The voltage at the voltage dividing point c between the resistors 5 and 6 are used as input signals. C is a low pass filter, 15,
It consists of 16 resistors and 17 capacitors. 20 is a comparator whose non-inverting input terminal receives the output signal of the inverting amplification circuit B in a low-pass manner.
The voltage is inputted via filter C, and a voltage corresponding to the set temperature of the vaporizing surface is inputted to the inverting input terminal. The voltage is obtained by dividing the voltage of the DC power supply 1 using resistors 21 and 22. 23 is a relay driven by the output of the comparator 20;
The vaporization heater (not shown) is turned on and off using the contacts to maintain the vaporization surface temperature near the set temperature. In addition, 25
27 is a capacitor, and 28 is a diode.

Further, the temperature distribution for generating a thermoelectromotive voltage of the thermocouple 2 is as shown in FIG. 2, where the vaporization surface (hot junction side) temperature is _T1 and the cold junction ambient temperature is _T2 . In the figure, V ₂ is a thermoelectromotive voltage generated between a and b due to the temperature difference between T ₁ and T ₂ . In temperature measurement using this thermocouple 2, even if the vaporizing surface temperature T ₁ is kept constant, if the cold junction ambient temperature T ₂ changes, the generated thermoelectromotive force V ₂ changes, and as shown in Figure 3, the thermoelectromotive voltage V 2 changes. The higher the contact ambient temperature T ₂ is, the lower the thermoelectromotive force V ₂ is (in Figure 3, T ₂ ′ to _{T 2} indicate the cold junction ambient temperature).
(The relationship is T ₂ ′<T ₂ ″<T _2. ) Therefore, when measuring temperature with a thermocouple, it is necessary to make a correction to remove the influence of the ambient temperature of the cold junction connected to the circuit.

In the circuit of this embodiment, this thermocouple correction is performed using the branch circuit A and the semi-fixed resistor 9 connected thereto, and at the same time, compensation adjustment for the offset voltage and current of the operational amplifier 11, temperature drift, etc. can also be performed. .

Next, operations for these adjustments will be explained.

First, if the voltage at the voltage dividing point c between the resistors 5 and 6 of the branch circuit A is _V1 , then when the cold junction ambient temperature _T2 increases, the resistance value of the thermistor ₈ decreases and the voltage increases, and vice versa. As T ₂ decreases, the voltage decreases, so its characteristics become as shown in the straight line shown in FIG.

On the other hand, the semi-fixed resistor 9 connected in parallel to the resistors 5 and 6 of the branch circuit A applies a variable voltage that is positive or negative to the voltage V ₁ at the connection point a between the movable part and the + pole side of the thermocouple 2. can be generated. Now, considering compensation for only the thermocouple 2, if the semi-fixed resistor 9 is adjusted so that the potentials at points a and c are the same, the thermoelectromotive voltage V ₂ will be reversed by the amplifying circuit B.
The voltage between the inputs is _V3 . The high voltage V ₄ between the input side point c and the output end point d of the inverting amplification circuit B is determined by the gain of the amplification circuit B, and there is a relationship of V ₄ =A·V ₃ , therefore, V ₄ =A· It becomes V ₂ . Then, the sum of the voltage V ₁ at the point c and the voltage V ₄ is the inverting amplifier circuit B.
The output voltage will be _V5 . From this, if we match the rate of change of voltages V ₁ and V ₄ due to the influence of ambient temperature, the characteristics of voltage V ₄ will become a straight line in Fig. 4, and therefore the influence of the cold junction ambient temperature will be canceled out, and the voltage V ₅ will be Since the characteristic is the straight line shown in FIG. 4, the output voltage _V5 is independent of the ambient temperature of the cold junction. In addition, since the correction of the cold junction ambient temperature by the surstar 8 takes into account the correction of the thermal electromotive voltage V ₂ and the correction due to the temperature drift of the inverting amplification circuit B, the circuit characteristics are affected by the cold junction ambient temperature. Things will disappear.

In addition, in order to increase the thermoelectromotive voltage, the operational amplifier 11
There is an effect of _offset voltage _and current of appear. Also, due to variations in the resistance of branch circuit A, V ₁
The voltage characteristics of V 4 become a straight line ′, and the voltage characteristics of V ₄ further change to a straight line. In order to remove the influence of these offsets, etc., the potential of the thermocouple point a relative to the voltage dividing point c can be adjusted by adjusting the semi-fixed resistor 9 in the same manner as the correction of the cold junction ambient temperature. Therefore, when correcting the effects of the cold junction ambient temperature and offset, etc., the semi-fixed resistor 9 is adjusted by taking into account the voltage change that combines the effects of both, and a
It is only necessary to adjust the potential at a point, and the correction operation can be performed extremely easily and accurately.

The output voltage _V5 from the inverting amplification circuit B obtained by this operation is applied to the non-inverting input terminal of the comparator 20 via the low pass filter C as a voltage _V7.
It is input as follows. On the other hand, the inverting input terminal of the comparator 20 has a resistor 2 corresponding to the set temperature.
A voltage V ₆ with a partial voltage ratio of 1 and 22 is input _, and _the voltage V ₆ and V ₇ are compared, and as shown in _FIG . )
In this case, the relay 23 is driven to energize the vaporization heater, and when V ₆ <V ₇ (the vaporization surface temperature T ₁ is higher than the set temperature), the energization to the vaporization heater is stopped.
Further, the above-mentioned fluctuation in the switching point E of the operation can be eliminated.

As described above, according to the present invention, all effects can be removed with a single operation of adjusting the resistance value of the semi-fixed resistor, so adjustment can be performed extremely easily and accurately, and the number of parts can be reduced. It is possible to obtain a thermo circuit with low cost and high reliability.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the vaporization heater thermocircuit according to the present invention, Fig. 2 is a temperature distribution diagram of the thermocouple of the same thermocircuit, and Fig. 3 is a diagram showing the temperature distribution of the thermocouple when the ambient temperature of the cold junction of the thermocouple is changed. A graph of thermoelectromotive voltage vs. measured temperature, FIG. 4 is a diagram showing voltage changes in various parts of the circuit with respect to changes in the ambient temperature of the cold junction, and FIG. 5 is a diagram showing the comparator input voltage relationship after adjustment. A... Branch circuit, B... Inverting amplifier circuit, C... Low pass filter, 2... Thermocouple, 8... Thermistor, 9... Semi-fixed resistor, 11... Operational amplifier.

Claims (1)

[Claims] 1 The signal from the thermocouple, which serves as a temperature sensor that measures the temperature of the combustor vaporization surface heated by the vaporization heater, is amplified by an amplifier circuit using an operational amplifier, and the amplified output is passed through a low-pass filter. is input to the comparator, and the comparator compares it with the voltage value corresponding to the set temperature of the vaporization surface to turn on the vaporization heater.
In the combustor vaporization heater thermocircuit configured to be turned off, a plant circuit consisting of a thermistor for detecting the ambient temperature of the cold junction of the thermocouple and a plurality of resistors is provided in parallel with the power input line of the operational amplifier in the amplification circuit; , connect a semi-fixed resistor so that positive and negative variable voltages can be extracted from the appropriate voltage dividing point voltage in the plant circuit, connect the movable terminal of the semi-fixed resistor to one end of the cold junction of the thermocouple, and create a thermoelectric A vaporization heater thermocircuit for a combustor, characterized in that the other cold junction of the pair and the voltage dividing point are connected to an input terminal of the operational amplifier.