JPS592823B2 - Water heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a water heater having both a can body corrosion prevention function and a dry firing prevention function.

In water heaters, it is well known to protect the can body from corrosion and to automatically prevent dry firing. Initially, the can body was used as a negative electrode, the corrosion protection electrode was used as a positive electrode, and a voltage of several volts was applied between the two. A so-called corrosion protection circuit that protects the can body from corrosion by applying water and, for example, a plurality of thermistors etc. attached to the can body in the vertical direction, detects the water level inside the can, and if the water level is lower than a predetermined water level, it will notify that fact. The so-called dry heating prevention circuits that display the display and stop the heating of water or hot water are electrically completely independent of each other, and recently attempts have been made to improve these circuits, At present, corrosion-proofing and dry-firing prevention circuits with a single electrode and a common circuit that share the flame detection electrode have been proposed.

A schematic diagram of this corrosion protection and dry firing prevention circuit will be explained with reference to FIG.

That is, in Fig. 1, 1 is the can body of the water heater, and 2, which is grounded, is an electrode disposed inside the can body 1 and electrically insulated from the can body 1, and as described later, a corrosion-preventing electrode. It also serves as a water level detection electrode.

3 is a corrosion protection power supply consisting of a constant voltage circuit, which outputs a corrosion protection voltage and also has a relay circuit that detects the water level and turns the contacts ON and OFF.

4 is a rectifier circuit having a step-down transformer; 5 is a combustion control circuit that controls supplying combustion to a combustor (not shown) based on a combustion command; controls sending combustion air to the combustor; ignition control;
Control to perform pre-purge, control to perform post-purge, control to stop fuel supply and air blowing to the combustor in the event of abnormal combustion or ignition failure, and heat water or hot water in the combustor in response to the output of the dry firing prevention circuit. This system performs various controls required for water heaters that use a combustor as a heat source, such as control to stop combustion for heating purposes.

6 is a blower that supplies combustion air to the combustor, 7 is a manual power switch, and 8 is a contact for controlling the blower 6, which is opened and closed based on various controls by the combustion control circuit 5 to supply combustion air to the combustor. It is closed when it is necessary to supply energy, and is open otherwise.

9 is a commercial AC power supply.

The one in Figure 1 has the above configuration, with an electrode 2 and a can body 1.
Corrosion protection of the can body 1 is carried out by the corrosion protection voltage of several V applied between the can body 1 and the water level inside the can body 1 becomes lower than the electrode 2, and the current (corrosion protection current) flowing from the electrode 2 to the can body 1 is Na(
Then, the relay circuit in the corrosion protection power source 3 is activated, and the combustion control circuit 5 is activated based on the activation of this relay circuit, and the supply of fuel to the combustion machine is stopped, and the contact 8 is opened and the blower 6 is turned on. It stops and combustion stops.

Further, if the water level in the can body 1 is below the electrode 2 at the time of starting combustion, combustion will not start.

That is, dry firing prevention is performed.

As is clear from the above explanation, the one in Fig. 1 has a water level judgment based on water level detection (whether it is below the set water level or above? Since the relay circuit is provided and its output further controls the combustion control circuit 5, the relay circuit requires a large power supply.

On the other hand, as is well known, the output of a corrosion-resistant circuit is several V1 and several hundred μ.
It's about eight.

Therefore, in the conventional circuit shown in FIG. 11, which uses the electrode 2 in common and uses anti-corrosion current to detect the water level and prevent dry firing, it is difficult to fully demonstrate the anti-corrosion function and to detect the water level reliably. difficult.

In particular, in water heaters, the water resistance changes depending on the quality and temperature of the water supplied into the can body 1, so the corrosion prevention function and dry boil prevention function can be fully demonstrated by taking this change in resistance into account. It is quite difficult to do so.

This invention was made in view of the existing circumstances,
It is an object of the present invention to provide a water heater that can sufficiently exhibit corrosion-proofing functions and dry-firing prevention functions, and can also suppress or prevent the effects of the potential of the dry-firing prevention upper electrode on the corrosion-proofing functions.

An embodiment of the present invention will be described below with reference to FIG.

- That is, in FIG. 2, 10 is a water level detection electrode, which is electrically insulated from the can body 1 by an insulator 11, and whose tip protrudes into the can body 1.

Reference numeral 12 is arranged inside the can body 1, and surrounds the tip of the water level detection electrode 10 at a predetermined distance with a shield having the same potential as the can body 1. The shield is made of a metal that is difficult to change in water quality and is still in the form of a mesh. It is formed.

Reference numeral 13 denotes a dry firing detection circuit which applies a voltage to the water level detection electrode 11, detects whether the water level inside the can body 1 is above a predetermined water level, and supplies its output to the combustion control circuit 5. .

14 is an insulator that electrically insulates the corrosion-proofing electrode 2 and the can body 1; 15 is, for example, an oil-burning combustor; 16 is a supply port that supplies water into the can body 1; and 17 is an insulator inside the can body 1. Floor number exit 18 from which hot water is taken out is the water surface.

Next, the operation of the embodiment shown in FIG. 2 will be explained.

With the water surface 18 at the solid line position, the power switch 7 is turned on and the operation switch (not shown) of the combustor 15 is operated to start combustion.

At this time, the dry firing detection circuit 13 detects that the water level in the can body 1 is above a predetermined level and supplies the signal to the combustion control circuit 5.
After K is determined, the contact 8 is closed, the blower 6 is rotated, and the inside of the combustor 15 is pre-purged, the supply of fuel to the combustor is started and ignition is started to start combustion. The water in the can body 1 is heated.

When the water in the can body 1 rises to a predetermined temperature, a temperature sensor (not shown) is activated and its output is supplied to the combustion control circuit 5, and the fuel supply to the combustor 15 is stopped. After a predetermined period of time, the contact 8 is opened and the post purge is completed.

On the other hand, during combustion, when the hot water in the can body 1 is used and the water surface 18 falls to the level indicated by the dashed line, that is, below the water level detection electrode 10, hot water flows from the water level detection electrode 10 to the can body.
The current that leads to this stops flowing, and the dry firing detection circuit 13 detects that the water level has fallen below a predetermined level, and its output is transmitted to the combustion control circuit 5, which controls the flow of fuel to the combustor 15. The supply of is stopped, and after a predetermined period of time, the contact point 8 is opened, and the post purge is also completed.

It goes without saying that water can be replenished into the can body 1 automatically by conventionally known means.

Corrosion protection is provided by a corrosion protection electrode 2.

As is clear from the figure, the corrosion protection electrode 2 is provided below the water level detection electrode, so even if the water level falls to a level that requires dry firing prevention, corrosion protection is independent of dry firing detection. to continue the corrosion protection operation.

As is clear from the above explanation, the one in FIG. 2 has a circuit configuration in which the dry firing detection circuit 13 does not become a load on the corrosion protection power supply 3, so the corrosion protection power supply 3 can fully demonstrate its corrosion prevention function. In other words, it is possible to take into account water quality fluctuations and water temperature fluctuations so that the corrosion protection function can be achieved even if there are considerable fluctuations, and the dry firing detection circuit 13 also takes into account the influence on the corrosion protection function. Sufficient power can be applied to the water level detection electrode 10 without any trouble, and it can be operated reliably.

In particular, if a shield 12 having the same potential as the can body P is provided, the voltage of the water level detection electrode 10 will not affect the corrosion protection electrode 2.

Note that there are various ways to derive power from the dry-burning detection circuit 13, but for example, power may be obtained from the secondary winding of a step-down transformer (not shown) in the rectifier circuit 4, and this secondary winding may be provided with a corrosion-resistant It is preferable to provide the secondary winding independently from the secondary winding that supplies power to the power supply 3.

As described above, the present invention provides a water level detection electrode separately from the corrosion protection electrode, and also provides a dry firing detection circuit separately from the corrosion protection power supply, and connects the power input terminal of the dry firing detection circuit to the corrosion protection power supply. In addition, the water level detection electrode is connected to the input side of the water level sensor, and a shield is provided to suppress or prevent it from affecting corrosion protection. It has the effect of reliably detecting empty firing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional water heater, and FIG. 2 is a schematic diagram showing an embodiment of the present invention. In the figure, 1 is a can body, 15 is a combustion machine, 5 is a control circuit,
2 is an electrode for corrosion protection, 3 is a power source for corrosion protection, 10 is a water level detection electrode, 13 is a dry firing detection circuit, and 12 is a shield. Note that the same reference numerals in the figures indicate the same or Wako parts.

Claims (1)

[Scope of Claims] 1. A control circuit that controls fuel supply to a combustor that heats water in the can and a blower that supplies combustion air to the combustor, and an electrical connection between the can and the can. The can body is protected from corrosion by applying a voltage from a corrosion protection power source between the can body and a corrosion prevention electrode provided insulated from the can body so that the can body has a low potential with respect to the electrode. In the apparatus equipped with a corrosion protection circuit and a dry firing prevention circuit that detects the water level in the can body and stops combustion in the heating reservoir of the combustor when the water level falls below a predetermined value, a water level detection electrode is provided separately from the above electrode. is electrically insulated from the can body and is provided inside the can body, and the power input terminal of the dry firing detection circuit of the dry firing prevention circuit is connected to the corrosion prevention power supply, which detects the water level by applying a voltage to the water level detection electrode. A water heater, characterized in that a shield is provided inside the can body, the shield being connected to the input side of the water level detecting electrode and suppressing or preventing the water level detection electrode from affecting the corrosion protection. 2. The water heater according to claim 1, wherein the water level detection electrode is disposed at a higher position than the corrosion protection electrode within the can body.