JPS6156930B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a thermocouple temperature measuring device.

As is well known, the output characteristics of a thermocouple have a non-linear relationship with temperature, so if the thermoelectromotive voltage output from a thermocouple is taken as temperature, an error will occur. As an example of a countermeasure, conventionally, when the output characteristic of a thermocouple is represented by a characteristic curve C in FIG. 3, this is approximated by a broken line connecting points P1, P2, P3, etc. with a straight line. According to this, each point can be considered to be in a proportional relationship, but in reality there is a difference between the curve C and each straight line, so it is important to avoid creating an error by that difference. I can't. Furthermore, since the proportionality constant must be selected depending on the magnitude of the thermoelectromotive voltage from the thermocouple, the configuration and operation become complicated.

An object of the present invention is to correct the thermoelectromotive voltage from the thermocouple in a thermocouple thermometer that uses a thermocouple to measure temperature with high precision and easily.

Embodiments of the invention will be described with reference to the drawings. 1 is an input terminal to which the thermoelectromotive voltage V from the thermocouple is input; 2 is a subtracter (analog subtracter); and 3 is a high-gain operational amplifier, which outputs an output corresponding to the temperature. 4 is a coefficient unit, 5 is an AD converter, 4 is a digital storage device such as ROM, 7 is a DA converter, 8
is an adder (analog adder), and 9 is a temperature output terminal.

Since the operational amplifier 3 has a high gain, the input voltage V
and the feedback voltage from adder 8 are equal in steady state. The coefficient value K of the coefficient unit 4 is determined as follows. That is, when the output characteristic of the thermocouple used in the target thermocouple is shown by curve C in FIG. 2, a straight line L is drawn that is sufficiently close to curve C. It is preferable that the straight line L intersects the curve C at at least one point, preferably two or more points. When the slope of this straight line L is K, this slope is taken as the coefficient value of the coefficient unit 4. In addition, the difference between the characteristic curve C and the straight line L in FIG.
Remember it. The number of quantized bits is the straight line L
If VN is made sufficiently close to curve C and VN is made sufficiently small, it can be made 8 bits or less.

The output of the operational amplifier 3 is given to a coefficient multiplier 4, where it is multiplied by K and output. The output of the operational amplifier 3 becomes the value of the straight line L at the temperature θ, that is, VL. Further, the output of the operational amplifier 3 is converted into a digital value by the AD converter 3. This digital value is given to the storage device 6 as address data. Here, VN for temperature θ is read out, and its digital value is
The signal is converted into analog by the DA converter 7. The outputs of the coefficient unit 4 and the DA converter 7 are added by an adder 8,
The added value is used as the feedback voltage in the subtracter 2.
given to.

In the above configuration, it is assumed that a thermoelectromotive voltage of V is now applied to the input terminal 1. At the beginning,
Assuming that the output of the operational amplifier 3 is a value smaller than θ, the output of the coefficient multiplier 4 at this time is the value vl of the straight line L.
(See Figure 2. The same applies hereinafter.) and the DA converter 7
The output is the difference vn between the curve C and the straight line L. Since the sum of both outputs vl and vn, that is, the output voltage of the adder 8, is smaller than the voltage V, the output of the operational amplifier 3 further increases. Finally, the output voltage of the adder 8 matches the voltage V. The output of the operational amplifier 3 at this time is nothing but the voltage θ, which coincides with P on the characteristic curve C. That is, since the operation is finally performed on the curve C, the output of the operational amplifier 3 can be directly used as the temperature output without any error.

The difference VN is stored digitally for the following reasons, in addition to the fact that digital values are easier to store than analog values. That is, as understood from the above explanation, it is necessary to store the difference VN for each temperature, and the higher the number of stored values, the higher the accuracy can be expected. However, if this is to be stored in an analog manner, if a capacitor is used as a storage element, a large number of such capacitors must be prepared. This makes the structure itself large and expensive. In this regard, when storing data digitally, an ultra-compact device with a large storage capacity such as ROM can be used as the storage device, so
The structure itself can be miniaturized and manufactured at low cost.
Also, as mentioned above, what is stored is the difference VN, which is a small value. Therefore, only a small number of bits are required to store one difference VN.
If the curve C is stored without using the straight line L, the same correction as in the present invention can be made, but the number of bits required to store the data for one curve will naturally be large, which is not preferable. do not have.

In reality, the thermoelectromotive voltage relative to the temperature of a thermocouple can be expressed by a general formula. Therefore, the difference between this characteristic curve and the straight line L can be easily calculated, and in the practice of this invention, the difference is calculated using an electronic computer. This calculation result may be stored in the storage device 6.

As detailed above, according to the present invention, when determining temperature from thermoelectromotive voltage, even if the characteristic curve of a thermocouple is nonlinear, it can be corrected without the conventional error, and the accuracy can be improved accordingly. In addition to making it possible to measure the temperature of
Furthermore, the number of bits required for storage can be reduced, resulting in an advantageous effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a characteristic curve diagram for explaining the operation, and FIG. 3 is a characteristic curve diagram for explaining the operation of a conventional example. 1...Input terminal, 2...Subtractor, 3...Arithmetic amplifier,
4...Coefficient unit, 5...AD converter, 6...Storage device, 7
...DA converter, 8...adder, 9...output terminal.

Claims (1)

[Claims] 1. A high gain operational amplifier that inputs a thermoelectromotive voltage, and the slope of a straight line that approaches the characteristic curve representing the relationship between the temperature of the target thermocouple and the thermoelectromotive voltage as a coefficient value, and the operational amplifier an inclinator that multiplies the output of the characteristic curve by a coefficient; a storage device that stores the digital value of the difference between the characteristic curve and the straight line for each temperature; and a storage device that stores the stored contents of the storage device in accordance with the output of the operational amplifier. An AD converter for an address for reading, a DA converter for outputting the contents read from the storage device, and feeding back the sum of outputs from the coefficient multiplier and the DA converter to the operational amplifier. A thermocouple temperature measuring device comprising a circuit, and using the output of the arithmetic amplifier as a temperature output.