JPS6316991Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a circuit that calculates the amount of heat required to heat a fluid to be heated to a desired temperature.

For example, in a combustion control system, the required amount of heat is There is a need for an arithmetic circuit that determines the size, and there is a desire to develop an arithmetic circuit with a simple configuration that can perform reliable arithmetic operations.

This idea was made in view of the above-mentioned requests, and is a simple required heat amount calculation that can calculate the amount of heat required to heat the fluid to be heated to a desired set temperature by analog calculation. The purpose is to provide circuits.

Next, an embodiment of this invention will be described with reference to the drawings. In FIG. 1, the temperature sensor Rd, which is a thermistor in this example, detects the temperature of the fluid to be heated before it is heated, and receives a constant current i1 from the constant current circuit 1, and its resistance value is determined by Rd.
If so, a voltage of f1Rd will be generated. Also, a temperature setting device Rs that sets the temperature of the heated fluid after heating.
receives a constant current i2 from the constant current circuit 2 and generates a voltage iRs according to its resistance value Rs.
In addition, the deviation amplifier composed of resistors R1 to R4 and operational amplifier U1 takes ε=i1Rd−i2Rs...(1) as input, and the amplification factor A is A=R2/R1...(2), then Aε= at the output terminal. Outputs the voltage expressed by R2/R1 (i1Rd−i2Rs) (3).

On the other hand, the transistor Q1 provided on the output side of the operational amplifier U1 is a switch circuit that operates on and off in response to the pulse of the flow rate signal, which is a pulse signal with a constant pulse width and a frequency proportional to the flow rate of the heated fluid. It consists of Also operational amplifier U
On the output side of 1, there are diodes D1, D2 and a resistor R.
A filter circuit consisting of 5, R6 and capacitor C1 is connected. This filter circuit has a diode D1 during the period when the transistor Q1 is off.
and resistor R5, transistor Q1
During the period when is on, the charge of capacitor C1 is transferred to resistor R
6 and diode D2, the terminal voltage of capacitor C1 is Ef=Aεts/tp=Aεtsf∝εf...(4) where f: frequency of flow signal tp: period of flow signal ts : Outputs an output signal expressed by the pulse width of the flow rate signal. In other words, the deviation amplifier, switch circuit, and filter circuit are
It operates as a multiplication circuit that calculates a voltage Ef proportional to (deviation between water supply temperature and set temperature) x (flow rate).
The result of this multiplication represents the amount of heat required to heat the fluid to be measured flowing at the measured flow rate to the set temperature.

The required amount of heat calculated in this manner is advantageously used, for example, in a combustion control device to control the amount of fuel supplied to the burner.
Alternatively, in an instantaneous water heater, it can be used to determine whether the water flow rate and outlet temperature settings are within the controllable range specific to the water heater. In other words, in an instantaneous water heater, the function of maintaining water flowing at a predetermined flow rate at a desired set temperature is
This can be achieved by adjusting the flow rate of fuel supplied to the burner, but the outlet temperature range and the outlet flow rate range are actually limited to the shaded range in FIG. In Figure 2, A is the unique maximum capacity curve determined by factors such as the maximum calorific value and thermal efficiency of the burner of the water heater, Q _L and Q _H are the lower and upper limits of the hot water output flow rate, and T _L and T _H are the The lower and upper limits are shown for the hot water temperature. Therefore, in the circuit shown in Figure 1, temperature sensor Rd detects the temperature of water supplied to the water heater, and an appropriate flow rate sensor detects the flow rate of water, thereby controlling temperature setting device Rs. The amount of heat required according to the set value can be determined, and from the detected value of the required amount of heat, it can be reliably known whether the set value of the temperature is within the controllable range shown in FIG.

As described above, according to this invention, the amount of heat required to heat the fluid to a desired set temperature can be easily determined by analog calculation based on the detected values of the temperature and flow rate of the fluid to be heated. can. Therefore, the circuit configuration is simple and can be constructed at low cost, and high reliability can be obtained. Further, when combustion control is performed based on the heat demand determined by this circuit, feed-forward control is performed, so that controllability is improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a heat requirement calculation circuit according to an embodiment of the invention, and FIG. 2 is a graph showing the controllable range of an instantaneous water heater. 1, 2...constant current circuit, Rd...temperature sensor,
Rs...Temperature setting device, U1...Operational amplifier.

Claims (1)

[Scope of utility model registration request] a temperature sensor that outputs a temperature signal of a voltage corresponding to the temperature of the heated fluid; a setting means that provides a set value signal of the temperature of the heated fluid; and a setting means that receives the temperature signal and the set value signal as inputs; a deviation amplifier that outputs a deviation signal corresponding to the difference between the two, a flow rate detector that generates a flow rate pulse signal with a constant pulse width and a frequency proportional to the flow rate of the heated fluid, and an output end of the deviation amplifier. a switch means connected to the flow rate pulse signal and controlled by the flow rate pulse signal; and when the switch means is in a first state, the deviation signal is applied, and when the switch means is in a second state, a predetermined voltage is applied thereto. a proportional circuit that outputs a voltage proportional to a value obtained by multiplying the difference between the temperature of the fluid to be heated and the set temperature by the flow rate of the fluid to be heated by smoothing the voltage of the fluid to be heated.