JP4457769B2 - Temperature control method for zirconia sensor - Google Patents

Description

  The present invention relates to a zirconia oxygen analyzer, and more particularly, to a zirconia oxygen analyzer that shortens the time from power-on to the start of measurement.

  In the zirconia oxygen concentration meter, it is necessary to control the surface temperature of the cell for detecting the oxygen concentration to, for example, 750 ° C. The temperature control uses a PWM function to output a rectangular wave power supply signal, but the duty ratio is controlled so that the temperature rise is constant.

FIG. 3 shows an example of a zirconia type oxygen concentration meter to which the present invention is applied. Reference numeral 1 denotes an oximeter main body, 2 denotes a zirconia type sensor, and 3 denotes a heater incorporated in the zirconia type sensor 2. The oxygen concentration meter main body 1 and the zirconia sensor 2 are connected by a sensor electromotive force signal line 4, a temperature signal line 5 and a power supply line 6. 7 is an oxygen concentration output signal line for outputting the oxygen concentration calculated based on the sensor electromotive force signal, and 8 is a contact input.

  FIG. 4 is a rectangular wave signal supplied from the power supply line 6 of FIG. 3 using the PWM function. For example, if the duty ratio is specified as 70% by software, the power ON time in one cycle is 70%, A heater output with a power off time of 30% can be realized. PID control is used from 700 ° C. to 750 ° C.

FIG. 5 shows a conventional warm-up example in which constant control is performed up to 700 ° C. with such a constant duty ratio.

  In addition, it is an apparatus suitable for performing program control such as a temperature in which such a set value has a predetermined gradient section and a fixed section, and is used for normal PID control and PID parameters and set values for improving disturbance response. There is a PID control having a function of temporally switching between two-degree-of-freedom PID control controlled with both PID parameters for suppressing overshoot at the time of change (see Patent Document 1).

Further, the temperature control system for performing image fixing an unfixed toner image by thermal contact with the heating body while maintaining a predetermined temperature range the heating body containing therein a heater across the first set temperature, the temperature T of the heater When the detected temperature T is equal to or lower than the first set temperature and the preset second temperature, the heating temperature is controlled so as to follow a set curve based on the difference temperature between the set temperature and the detected temperature The first control means is selected, and when the detected temperature exceeds the second temperature, the second control means is selected to control the heating body so as to become the first set temperature ( Patent Document 2).

Japanese Patent Laid-Open No. 6-187005 Japanese Patent Publication No. 8-328423

By the way, in the conventional zirconia oximeter, constant control was used up to 700 ° C.
The constant control means that the heater is output at a constant duty ratio up to 700 ° C, and the software only needs to acquire the current temperature and specify the constant duty ratio, so the software load required for temperature control is small. Is excellent. However, when the temperature is low, the temperature rises greatly, and as the temperature rises, the temperature rises gradually. Therefore, depending on the environment, the temperature may not rise to 700 ° C., and the measurable state (750 ° C.) is reached. It was a problem that the time until could not be predicted.

  Therefore, the problem to be solved by the present invention is to realize a feedback control (hereinafter referred to as gradient control) with a fixed temperature increase rate (for example, 1 ° C./1 second), so that the temperature can always be increased to 700 ° C. and can be measured. Be able to predict the time to reach the state. It is another object of the present invention to provide software that is simpler than PID control and requires less software load for temperature control.

In order to solve such a problem, the invention of claim 1 among the present invention,
A partition is made of a solid electrolyte ceramic of stable zirconia, a gas permeable porous platinum electrode is formed on both sides of the partition, and a heater for detecting oxygen concentration is introduced on both sides of the partition by introducing gases having different oxygen partial pressures. In the temperature control method of the zirconia sensor ,
Current and obtaining a temperature of the zirconia sensor,
A step of comparing the acquired current temperature with the set temperature;
If the acquired current temperature is lower than the set temperature, the difference between the temperature calculated by multiplying the predetermined rate of temperature increase by the elapsed time from the start of heating and the actually measured temperature until the set temperature is reached, and the same calculation Changing the heating control amount of the heater according to the amount of change in the temperature difference from the previously measured temperature, and performing a temperature increase rate gradient control process by feedback control that fixes to a constant temperature increase rate ; and
A process of performing control by PID if the acquired current temperature has reached the set temperature;
A temperature control method for a zirconia sensor .

In claim 2, in the temperature control method of the zirconia sensor according to claim 1,
Until the set temperature is reached, the current temperature rise rate gradient control amount is obtained by the following equation at a constant cycle.
This temperature increase rate gradient control amount = previous temperature increase rate gradient control amount +
K1 × (s × t−T (t)) + K2 × Δ (s × t−T (t))
t: Elapsed time from the start of heating s: Rate of temperature increase per fixed time T (t): Actually measured temperature (varies depending on the elapsed time from the start of heating)
Δ (s × t−T (t)): difference between the current time and the previous time regarding s × t−T (t) K1, K2; coefficients for correcting individual differences between devices

The present invention has the following effects. According to the temperature control method of the zirconia sensor according to claim 1 and 2,
Until the set temperature is reached, the temperature gradient is controlled by the rate of temperature rise per fixed time, and the temperature calculated by multiplying the temperature rise rate per fixed time by the elapsed time from the start of heating and the actually measured temperature Since the amount of heating control is changed according to the difference and the amount of change in the previous temperature difference calculated in the same way, the temperature can always be increased to the set temperature (700 ° C in this case) and measurement is possible. It will be possible to predict the time to reach the state.
Also, from the viewpoint of software, the software is simpler than PID control, so that the software load required for temperature control is excellent.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a flowchart showing an example of temperature control of a zirconia oximeter according to the present invention. This will be described according to the flow.
When control is started by turning on the power or the like (start), the current temperature is acquired via the temperature signal line 5 in step 1 (see FIG. 3).
Next, in step 2, the measured temperature and the set temperature (700 ° C.) are compared by a calculation means (not shown) provided in the oximeter main body 1.

As a result of comparison, if the temperature reaches 700 ° C., control by PID is performed, and if the temperature is less than 700 ° C., gradient control processing is executed. That is, a numerical value obtained by calculating the difference between the set temperature and the current temperature and multiplying it by a specific constant (first-order coefficient) is added or subtracted from the previous heater control amount.

However, this alone causes a response delay of the temperature value (the time from when the heater control amount is changed to when the changed temperature value is read), and thus overshoot occurs. Therefore, the amount of change in the temperature difference between the current temperature and the set temperature (temperature increase rate difference) is calculated, and a numerical value obtained by multiplying it by a specific constant (secondary coefficient) is added or subtracted. In the experiment, the current value was obtained every 5 seconds. As a result, the temperature increase every 5 seconds can be known, and a constant temperature increase rate (for example, 1 ° C./1 second) can be realized.

Current gradient control amount = previous gradient control amount +
K1 × (s × t−T (t)) + K2 × Δ (s × t−T (t))
t: Elapsed time from the start of heating s: Rate of temperature increase per fixed time T (t): Actually measured temperature (varies depending on the elapsed time from the start of heating)
Δ (s × t−T (t)): Difference between current time and previous time regarding s × t−T (t) K1, K2; coefficients for correcting individual differences of devices.

FIG. 2 is a diagram illustrating a state in which warm-up is started in a state of room temperature T, and gradient control up to a predetermined temperature (700 ° C.) and PID control after reaching 700 ° C. are performed.
Therefore, according to the present invention, the temperature can be surely increased to a predetermined temperature even in a cold region, and the time until measurement can be performed can be predicted.

  The above description merely shows a specific preferred embodiment for the purpose of explaining and illustrating the present invention. For example, the set temperature is not necessarily 700 ° C. Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

It is a principal part block diagram which shows one Example of the control flow of the zirconia type oxygen concentration meter of this invention. It is explanatory drawing explaining the Example of gradient control and PID control. It is a block diagram which shows an example of the zirconia type oxygen concentration meter by which this invention is implemented. It is explanatory drawing which shows the example of control by a duty ratio. It is explanatory drawing which shows the example of control of the conventional zirconia-type oxygen concentration meter.

Explanation of symbols

1 Oxygen concentration meter body 2 Zirconia sensor 3 Heater 4 Sensor electromotive force signal line 5 Temperature signal line 6 Power supply line 7 Oxygen concentration output signal line 8 Contact input

Claims (2)

A partition is made of a solid electrolyte ceramic of stable zirconia, a gas permeable porous platinum electrode is formed on both sides of the partition, and a heater for detecting oxygen concentration is introduced on both sides of the partition by introducing gases having different oxygen partial pressures. In the temperature control method of the zirconia sensor ,
1) a step of acquiring the current temperature of the zirconia sensor,
2) comparing the acquired current temperature with the set temperature;
3) If the acquired current temperature is less than the set temperature, the difference between the temperature calculated by multiplying the predetermined rate of temperature rise by the elapsed time from the start of heating and the actually measured temperature until the set temperature is reached, and Similarly, the process of changing the heating control amount of the heater according to the amount of change of the temperature difference from the previously measured temperature and performing the temperature increase rate gradient control process by feedback control that fixes to a constant temperature increase rate ;
4) A process of performing control by PID if the acquired current temperature has reached the set temperature,
A temperature control method for a zirconia sensor . 2. The temperature control method for a zirconia sensor according to claim 1, wherein the current temperature rise rate gradient control amount is obtained by the following formula at a constant period until the set temperature is reached .
This temperature increase rate gradient control amount = previous temperature increase rate gradient control amount +
K1 × (s × t−T (t)) + K2 × Δ (s × t−T (t))
t: Elapsed time from the start of heating s: Rate of temperature increase per fixed time T (t): Actually measured temperature (varies depending on the elapsed time from the start of heating)
Δ (s × t−T (t)): difference between the current time and the previous time regarding s × t−T (t) K1, K2; coefficients for correcting individual differences between devices

Images