JPH0551826B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an average temperature detection device for a hot water storage tank in an electric water heater, for detecting the average temperature of water in the hot water storage tank.

BACKGROUND OF THE INVENTION Electric water heaters are commonly equipped with a so-called boiling temperature control system in order to boil water most efficiently based on the amount of hot water used each day.

The most direct way to measure the amount of hot water used is to measure the amount of water supplied or the amount of hot water supplied.
Since flow rate systems are expensive, a widely known method is to indirectly measure the amount of hot water used by detecting the average water temperature in a hot water storage tank.
In other words, when the hot water tank of an electric water heater is generally supplied with hot water from the hot water supply pipe at the top, the same amount of water is replenished from the water supply pipe at the bottom, and the tank is always kept full of water. By measuring the average water temperature in the hot water storage tank, the amount of hot water to be supplied can be easily calculated from the energy balance.

Therefore, as a conventional means of detecting average water temperature,
It was common practice to install a plurality of temperature sensors at appropriate intervals in the vertical direction of the hot water storage tank, read the output of each temperature sensor, and then calculate the arithmetic average of the outputs.

Problems to be Solved by the Invention Accordingly, when using such conventional technology, in order to accurately detect the average water temperature in the hot water storage tank,
At least several to a dozen temperature sensors must be prepared and the output signals of each must be input to a microcomputer, etc. for calculation, which increases the overall cost.
Since the number of input ports for the microcomputer must be equal to the number of temperature sensors, there is an unavoidable problem that a so-called one-chip type microcomputer cannot be used.

Therefore, in view of the actual state of the prior art, an object of the present invention is to attach temperature sensors to the upper and lower parts of the hot water storage tank, while reading the average temperature of the intermediate part all at once using a diode. Since a diode is used instead of a temperature sensor, the overall cost can be significantly reduced, and the number of input ports required for the microcomputer is reduced to 3, the upper and lower temperature sensors and the middle diode. An object of the present invention is to provide a new average temperature detection device for a hot water storage tank in an electric water heater, which can be sufficiently handled by a one-chip microcomputer because the temperature can be reduced to just a few.

Means for Solving the Problems The configuration of the present invention to achieve the above object includes temperature sensors attached to the upper and lower parts of the hot water storage tank, and diodes attached so as to equally divide the installation interval between the temperature sensors. , a controller that inputs each output signal of the temperature sensor and a forward voltage drop signal of a series circuit of diodes and calculates the average value of the temperature indicated by each of these signals. The gist is to calibrate the temperature indicated by the forward voltage drop signal when the difference in the indicated temperatures is small.

With this configuration, the temperature sensor can correctly detect the water temperature at the top and bottom of the hot water storage tank, while the diode
Since the temperature sensors are installed so that the installation interval is equally divided, the forward voltage drop signal of the series circuit displays the total value of the forward voltage drop of each diode corresponding to the temperature at the installation position of each diode. be able to. Here, since the forward voltage drop of a diode generally decreases linearly with temperature, the forward voltage drop signal obtained in this way can be a signal indicating the average temperature at the mounting position of each diode. Therefore, by calculating the average value of the temperature indicated by the output signal of the temperature sensor and the temperature indicated by the forward voltage drop signal, the average temperature in the hot water storage tank can be obtained.

In addition, diodes generally have large variations in forward voltage drop from element to element, but this variation is
When the water temperature in the hot water storage tank can be considered to be almost uniform, it can be effectively corrected by calibrating the temperature indicated by the output signal of the temperature sensor, so an inexpensive diode can be used instead of the temperature sensor. Even if , the measurement accuracy can be maintained as high as necessary.

It works as described above.

Example Examples will be described below with reference to the drawings.

The average temperature detection device of the hot water storage tank in an electric water heater includes temperature sensors S ₁ and S ₂ disposed at the upper and lower parts of the hot water storage tank 11 of the electric water heater 10, and an intermediate portion between the temperature sensors S ₁ and S ₂ . , a plurality of diodes D ₁ , D ₂ , etc. arranged in the vertical direction, and a controller 21 (FIG. 1).

The hot water storage tank 11 has an electric heater 12 installed in its lower part, and has a water supply pipe 11a connected to its bottom.
It is a cylindrical sealed container with a hot water supply pipe 11b connected to the top surface, and when hot water is discharged from the hot water supply pipe 11b, the same amount of water is replenished through the water supply pipe 11a, so that it is always used in a full state. shall be.

The temperature sensors S ₁ and S ₂ are, for example, thermistor-type temperature detection elements, and can be attached to the upper and lower walls of the hot water storage tank 11 to detect the temperature of the water in the hot water storage tank 11 at the mounting device. shall be taken as a thing.

The diodes D ₁ , D ₂ ... may be general rectifier diodes, and multiple diodes should be placed at equal intervals so as to equally divide the vertical installation distance between the temperature sensors S ₁ and S ₂ . , shall be installed in the vertical direction. Diodes D ₁ , D ₂ ... are temperature sensors
Like S ₁ and S ₂ , they are attached to the wall of the hot water storage tank 11 so that the water temperature inside the tank 11 is well transmitted.

The controller 21 consists of a combination of an AD converter 21a and a microcomputer 21b.
The output signals S _{1 a, S 2 a of the temperature sensors S 1 , S 2} and the forward voltage drop signals Sda from the diodes D ₁ , D ₂ . . . are input to the controller 21, and the AD converter 21
It is assumed that the data is read by the microcomputer 21b via a.

When using a thermistor as the temperature sensor S ₁ , S ₂ , the output signals S ₁ a, S ₂ a are generated by the resistance R ₁ , R ₂
The signal is input to the AD converter 21 via an auxiliary circuit consisting of (Fig. 2). That is, one end is connected to the reference voltage power supply V, and the other end is connected to temperature sensors S ₁ and S ₂ through a resistor R _2. A span adjustment resistor R ₁ is connected in parallel to the temperature sensor S 1 and S 2 . From the connection point between sensors S ₁ and S ₂ and resistor R ₂ , the output resistance
Output signals S ₁ a and S ₂ a are extracted via R ₃ .

On the other hand, all of the diodes D ₁ , D ₂ . . . are connected in series, and the anode side is connected to the reference voltage power supply V, and the cathode side is grounded via the constant current device CI (FIG. 3). A protection diode Dp of opposite polarity is connected in parallel with the series circuit of diodes D ₁ , D ₂ ..., while a forward voltage drop signal Sda is generated from the connection point between the diodes D ₁ , D ₂ ... and the constant current device CI. , is brought out via the output resistor _R4 .

The operation of the average temperature detection device having such a configuration is as follows (FIG. 4).

First, the program in the microcomputer 21b of the controller 21 reads the output signals S _{1 a} and S ₂ a of the temperature sensors S ₁ and S ₂ and converts them into temperature signals.
Convert to Ts ₁ and Ts ₂ (step (1) in Fig. 4, hereinafter simply referred to as (1)). Next, read the forward voltage drop signal Sda of the diodes D ₁ , D ₂ ...,
Let 1/n of that size be the forward voltage Vd (2).
However, n is the number of diodes D ₁ , D ₂ . . . connected in series.

Next, convert the forward voltage drop Vd to temperature Td
(3). Now, assuming that the temperature characteristics of the forward voltage drop of each of the diodes D ₁ , D ₂ , etc. are represented by straight lines 1, 2, and so on in Fig. 5, the average characteristics are as shown in the lines 1, 2, and so on. It can be represented by a dashed line N obtained by plotting the average value. However, straight lines 1, 2... show the characteristics when the forward currents of the diodes D ₁ , D ₂ ... are maintained at a constant value by the constant current device CI, and generally the diodes D If the ratings of ₁ , D ₂ . . . Therefore, the temperature Td corresponding to the forward voltage drop Vd can be uniquely determined using the dashed line N, and this temperature Td
may indicate the average value of each temperature at the mounting positions of the diodes D ₁ , D ₂ .

Next, the program determines whether the difference between the temperatures Ts ₁ and Ts ₂ indicated by the output signals S ₁ a and S ₂ a of the temperature sensors S ₁ and S ₂ is sufficiently small (4), and determines whether this difference is a predetermined value. When it is smaller than the value a, calibration is performed for the temperature Td indicated by the forward voltage drop signal Sda from the diodes D ₁ , D ₂ . . . ((5), (6)). That is, temperature sensors S ₁ , S ₂
are attached to the upper and lower parts of the hot water storage tank 11, and when the temperatures Ts ₁ and Ts ₂ are sufficiently close to each other, the temperature Td in the middle part is a temperature Ts ₁ that is somewhat lower than the temperature Ts ₁ in the upper part. -b (however, 0
Since it should be <b<a), the temperature Td and the temperature
Store the difference between Ts ₁ - b as the calibration amount △.
(5), this calibration amount △ is used to obtain an accurate value for the temperature Td (6). When the difference between the temperatures Ts ₁ and Ts ₂ is larger than the predetermined value a, the previously determined calibration amount Δ may be used repeatedly ((4), (6)).

Using the temperatures Ts ₁ , Ts ₂ , and Td thus obtained, the average temperature Tav in the hot water storage tank 11 can be obtained (7). However, here the temperature Td
represents the average temperature _{of the} mounting positions of n diodes D ₁ , D ₂ .

In the above description, it goes without saying that the temperature sensors S ₁ and S ₂ are not limited to thermistor-type temperature detection elements, but any other type of temperature sensor including a thermocouple can be used. Also, the diode
The number n of D ₁ , D ₂ . , the average temperature Tav can be detected with higher accuracy.

Effects of the Invention As explained above, according to the present invention, temperature sensors are attached to the upper and lower parts of the hot water storage tank, and the average temperature in the middle part of these temperature sensors is detected by the forward voltage drop of the diode. By calibrating the temperature indicated by the diode forward voltage drop signal when the difference in temperature detected by the temperature sensor is sufficiently small, the temperature sensor can be replaced with
Since low-cost diodes can be used, the overall cost can be significantly reduced, and the number of input ports on the controller can be adjusted to accommodate the upper and lower temperature sensors regardless of the number of diodes used. A total of 3 items are enough, including
This has the excellent effect of making it easy to configure a controller using a one-chip microcomputer.

[Brief explanation of the drawing]

1 to 5 show an embodiment, FIG. 1 is a general schematic diagram, FIG. 2 is a thermistor input circuit diagram, FIG. 3 is a diode input circuit diagram, and FIG. 4 is a program flowchart. FIG. 5 is a graph showing an example of the temperature characteristics of a diode. S ₁ , S ₂ ... Temperature sensor, D ₁ , D ₂ ... Diode, S ₁ a, Sa ₂ ... Output signal, Sda ... Forward voltage drop signal, Ts ₁ , Ts ₂ , Td ... Temperature, 10 ...Electric water heater, 11...Hot water tank, 21...Controller.

Claims (1)

[Claims] 1. Temperature sensors attached to the upper and lower parts of the hot water storage tank, diodes attached so as to equally divide the mounting interval of the temperature sensors, an output signal of the temperature sensor, and a forward voltage drop signal of the series circuit of the diodes. and a controller that calculates the average value of each temperature indicated by the output signal and the forward voltage drop signal, and the controller calculates the forward voltage drop when the difference between the temperatures indicated by the output signal is small. An average temperature detection device for a hot water storage tank in an electric water heater, characterized in that the temperature indicated by the signal is calibrated.