JPS6011299B2 - temperature control device - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in fluid temperature control.

A conventional temperature control device will be explained with reference to FIG. 1, taking as an example an instantaneous water heater using an electromagnetic proportional control valve.

In FIG. 1, reference numeral 1 denotes a heat exchanger, which together with a burner 4 constitutes a heating means, which exchanges the combustion heat of the burner 4 with boiled water that enters from a water pipe 2, and supplies hot water from a water tap 3. Gas is supplied to the gas burner via a gas pipe 6 and an electromagnetic proportional control valve 5. The electromagnetic proportional control valve 5 continuously changes the valve opening depending on the amount of current flowing through the built-in coil.
There is a device that controls gas proportionally, and its characteristics are shown in Figure 2. The vertical axis 0 is the gas flow rate, the horizontal axis 1 is the coil current,
The amount of gas changes in proportion to the amount of current. Conventionally, the overflow of hot water is detected by a negative temperature-sensitive resistance element (hereinafter referred to as a thermistor) which is a temperature detection means installed at the exit point of the heat exchanger, and its output is transmitted to the heating means together with the electromagnetic proportional control valve 5. It is applied to the coil of the electromagnetic proportional control valve 5 through the comparator amplifier 7, which constitutes a control means that controls the amount of gas heated and controls the temperature of the fluid, and controls the amount of gas to maintain a constant temperature. There was a stability problem.

Therefore, a conventional concrete circuit of the comparator amplifier 7 is shown in FIG.
8 is a power supply, and the thermistor × and fixed resistors 13, 1
4 and 17 form a bridge, and the midpoint potential is compared by the transistor 15.

When the overflow of hot water is low, the resistance value of the thermistor X is large, so the transistor 15 is energized, and the current is amplified by the transistor 11 to flow through the coil 10' of the electromagnetic proportional control valve 5. The lower the outlet temperature is than the set temperature, the larger the current is, the more the combustion amount increases, and the closed loop control raises the outlet temperature to the set temperature. The fixed resistor 16 is the base resistance of the transistor 1, the fixed resistor 12 is the emitter resistance of the transistor 11, and the diode 9 is for absorbing the back electromotive force of the coil 10. The control characteristics in this case are shown in FIG.

The vertical axis shows the temperature detected by the thermistor x (hot water supply temperature) Tx, the amount of hot water supplied at that time is shown as W, and the horizontal axis shows the elapsed time as t. Now, it is assumed that the amount of hot water supplied is n and the detected temperature at that time is stable until time 0 is reached.
When the hot water supply amount is changed to m at time ○, the detected temperature does not rise immediately due to a delay in the heat exchanger, and the conventional combustion amount is maintained during that time. As a result, after some time has elapsed, the detected temperature suddenly rises, and the combustion amount is reduced accordingly, but the combustion amount is excessively reduced while the temperature is higher than the set temperature n. In the meantime, the detected temperature decreases, but because of the above-mentioned excessive throttling, it continues to decrease even after reaching the set temperature. The combustion amount increases accordingly, and an excessive combustion amount is supplied while the temperature is lower than the set temperature n.
In the meantime, the detected temperature rises, but due to the above-mentioned excessive combustion amount, it continues to rise even after reaching the set temperature. After repeating this, it gradually decreases and stabilizes at the set temperature n, but
If the pulsation time is long and extreme, the pulsation will continue forever. In other words, in this conventional configuration, the detected temperature always works to match the set temperature, but has the drawback of extremely poor stability.

In order to shorten the time, there is also a method of providing a means for detecting the fluid flow rate, that is, the amount of hot water supplied, and changing the combustion amount based on the flow rate signal. A conventional example is shown in FIG. In order to detect the amount of hot water supplied, an orifice 18 is formed in the hot water supply pipe, and a pressure sensor Y detects the differential pressure before and after and converts it into a change in resistance value.
There is one that controls the combustion amount using the signal from the thermistor X and the signal from the thermistor X. FIG. 6 shows a specific circuit example. Unlike FIG. 3, a pressure sensor Y is connected in series with the thermistor X, and the output changes even when the amount of hot water supplied changes in addition to temperature changes. For example, when the amount of hot water supplied decreases, the differential pressure decreases, and the resistance value of the pressure sensor Y decreases, reducing the current to the coil 10 and lowering the combustion amount. The characteristics in this case are shown in FIG. Since changes in the total amount of hot water appear as changes in the regular combustion amount, the range of temperature fluctuations is small and it takes less time to reach stability. However, since the temperature signal is combined with a hot water supply amount signal, which is not directly related to temperature control, to perform closed-loop control of the temperature, the temperature setting changes depending on the magnitude of the hot water supply amount signal, and the temperature changes to the set temperature. It deviates from n by p and becomes stable.

The value of this deviation p varies depending on the magnitude of the hot water supply amount signal and the control system, and can be positive or negative. In addition to pressure sensors, there are devices that directly detect the flow rate based on the rotation speed of the propeller installed in the hot water pipe, and control circuits that determine the amount of hot water to be heated by multiplying it by the difference in temperature between the inlet and outlet of the heat exchanger. Although there are some complicated ones such as the following, a temperature deviation p occurs in all of them. However, in many cases what is actually desired to control is temperature, and this is particularly undesirable in shower temperature control as the layers are sensitive to changes even by a few degrees. The present invention uses a flow rate signal to perform stable control, but the closed-loop control is performed using temperature to solve the above-mentioned drawbacks.

FIG. 8 shows a circuit according to an embodiment of the present invention.

The difference from FIG. 3 is that the connection point between the thermistor x and the fixed resistor 17 and the connection point between the pressure sensor Y' and the fixed resistor 19 are connected by a capacitor 20. In this configuration, the flow rate signal corresponding to the magnitude of the flow rate change detected by pressure sensor Y is added to the temperature signal of thermistor change.

Therefore, temperature changes due to flow rate changes are reduced,
This also shortens the time it takes to reach stability. However, when both the flow rate and temperature are stabilized, the current flowing through the capacitor 20 is zero, and regardless of the value of the pressure sensor Y, the set temperature can be obtained by closed loop control determined by thermistor x and fixed resistors 13, 14, and 17. .

The characteristics at that time are shown in FIG.

In Figure 9, as in Figure 7, the temperature fluctuation range is small, and it takes a little time to reach stability. Moreover, the stable temperature settles down to the set temperature n. As described above, by using the temperature control of the present invention, the stability of control is dramatically improved without affecting the control temperature.

The above has been explained using an instantaneous water heater for hot water supply as an example.
The same applies to a gas furnace as shown in FIG.

Components with the same numbers as in FIG. 1 have the same functions. 21 is a furnace outer body.

Combustion heat passes through the heat exchanger 1 and is exhausted from the exhaust stack 22, but the heat is exchanged with air sent from the blower 23 and hot air is supplied from the blower outlet 23'. In the furnace, the temperature of the hot air from the outlet 23' is controlled.
A thermistor The present invention works effectively regardless of the type.

In addition, although we have explained using an electromagnetic proportional valve as an example of a fuel control valve, it is effective not only in continuous control but also in multi-step control, and even if the heat source is a heater. The present invention can be employed simply by connecting a heater instead of the coil, and the spirit of the present invention is not limited by the equipment or heat source. As described above, the temperature control device of the present invention includes a fluid heating means, a means for detecting the flow rate of the fluid, a means for detecting the fluid temperature after heating by the heating means, and a flow rate signal from the flow rate detecting means. The value of the flow rate signal is controlled by controlling the heating amount of the heating means using the input as input, and performing open loop control to match the temperature signal from the temperature detection means with a set value configured independently of the flow rate signal. Since it has a control means that controls the temperature of the fluid to the set value regardless of the flow rate, the temperature changes due to changes in flow rate are reduced, thereby shortening the time it takes to reach stability.Moreover, when the temperature is stable, the temperature remains as set. It has the advantages that can be obtained.

[Brief explanation of drawings]

Figure 1 is a temperature control configuration diagram of a secondary instantaneous water heater, Figure 2 is a characteristic diagram of the electromagnetic proportional control valve used in Figure 1, Figure 3 is a conventional temperature control circuit diagram, and Figure 4. is the conventional temperature control characteristic diagram,
Fig. 5 is a block diagram showing another example of the temperature control block diagram of an instant boiler, Fig. 6 is a diagram showing another example of a conventional temperature control circuit, and Fig. 7 is a diagram showing another example of a temperature control circuit diagram of an instantaneous boiler. FIG. 8 is a temperature control circuit diagram in an embodiment of the present invention, FIG. 9 is a temperature control characteristic diagram thereof, and FIG. 10 is a temperature control configuration diagram when used in a gas furnace. DESCRIPTION OF SYMBOLS 1... Heat exchanger, 4... Gas burner (constituting heating means together with 1), 5... Electromagnetic proportional control valve, 7... Comparative amplifier (constituting control means together with 5), 10 ... Coil of electromagnetic proportional control valve, 113, 14, 17... Fixed resistor, 15... Transistor, 20... Capacitor, X... Negative temperature sensitive resistance element (temperature detection means), Y'... Pressure sensor (flow rate detection means). Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] 1 A fluid heating means, a means for detecting the flow rate of the fluid, a means for detecting the fluid temperature after heating by the heating means, and a flow rate signal from the fluid detecting means is input to control the heating amount of the heating means. At the same time, the temperature of the fluid is controlled to the set value regardless of the value of the flow rate signal by performing closed loop control to match the temperature signal from the temperature detection means with a set value configured independently of the flow rate signal. A temperature control device having a control means.