GB2109097A - Improvements in water heating arrangements - Google Patents

Abstract

A machine having an electric water heater the temperature of which is monitored by a temperature sensor to control a heating cycle, an output derived from the sensor to control a course of a heating cycle is compared with at least one fixed reference level, and an electronic switch is operated to switch on an alarm device and/or to cut off the supply of heating current and/or to divert the supply of heated water if the said output is above a predetermined threshold.

Description

SPECIFICATION Improvements in water heating arrangements This invention relates generally to a water heating arrangement, and in particular to a device in such an arrangement for avoiding risk of damage due to build up of scale. The invention is especially applicable to water heaters which are used on an intermittent basis, such as coffee making machines, in which the temperature of an electric heater is monitored to control a heating cycle.

In accordance with the invention, in a machine having an electric water heater the temperature of which is monitored by a temperature sensor to control a heating cycle, an output derived from the sensor during the course of a heating cycle is compared with at least one fixed reference level, and an electronic switch is operated to switch on an alarm device and/or to cut off the supply of heating current and/or to divert the supply of heated water if the said output is above a predetermined threshold.

The invention relies for operation on the fact that the temperature, rate of change of temperature, or indeed rate of rate of change of temperature, at a selected point in the heater at a given time in the heating cycle, will have a value dependent on the amount of accumulated scale. The output derived from the sensor at this given time, dependent on one of the stated parameters, is compared with the at least one reference level.

In a preferred arrangement, the temperature is sensed at a fixed time after the start of the heating cycle. If the sensed temperature is below a first reference level, the cycle is deemed normal; if above a first reference level but below a second higher reference level, the heater is deemed partially scaled and a warning indicator is activated; if above the second reference level but below a third reference level the heater is deemed scaled and the heating cycle may be interrupted or modified and/or a second alarm indicator activated.

The third reference level is the temperature sensed by continuous monitoring towards the end of the heating cycle, the attainment of which indicates that the heater is dry due to completion of water heating.

As previously indicated, the invention is especially applicable to coffee-making machines, and is particularly useful in a coffeemaking machine having a diverting valve whereby heated water can be diverted from its normal coffee-making path. In such a case, an output above the second reference level may cause activation of the diverting valve, so that no further coffee can be made until the machine has been de-scaled to avoid damage which could be caused by further usage.

Moreover, in such a machine, it will be possible to operate the heater with the diverting valve activated, so that de-scaling can readily be carried out by heating water containing the conventional additive crystals, without passing the de-scaling water through the part of the machine which normally brews the coffee, e.g. filter cup and jug.

Thus, according to a further aspect of the invention, there is provided a coffee-making machine having a diverting valve which when activated diverts water into an alternative path to the path through the coffee-making part (i.e. filter cup) of the machine and also having an electric heater associated with a sensor which monitors the temperature of the heater to control a coffee-brewing cycle, wherein a device is provided to detect scale build-up, said device comprising a timer which, at a given time after the start of a heating cycle, initiates a scale detection function, a comparator which when said detection function is initiated receives an output derived from the temperature sensor and compares said output with at least one reference level, and circuit means for activating the diverting valve if a reference level designating a scaled up heater is exceeded.

A practical arrangement of coffee-making machine in accordance with the invention will now be briefly described by way of example.

The basic machine is of a conventional form, with a base having on one side an electrically heated plate on which a coffee jug stands and having on the other side an upstanding arm structure which overhangs the coffee jug, leaving space therebetween for the interposition of a coffee filter cup. The arm structure contains a water reservoir the lower section of which contains an electric heater element. The water heater section may conveniently be in the form of a U-tube with one leg wider than the other, the electric heater element receiving to heat water in the wider leg so that, due to the creation of bubbles of steam, the water density in this leg is lowered and water therein rises into a delivery pipe, wherein the heated water is delivered laterally over the filter cup.

The lateral path from the reservoir to the outlet to the filter cup is interrupted by a valve which, when activated, closes the path of the outlet to the filter cup and diverts water to an alternative outlet. Heated water can be collected from this alternative outlet, but not via the coffee brewing part of the machine, i.e.

via the filter cup. Thus, when thes said valve is activated, the machine is no longer usable for brewing coffee.

The machine has a temperature sensor in the heater section, preferably at or near the top thereof. When the machine is switched on, a chosen amount of cold water filled into the reservoir is heated and delivered over the filter cup, to filter through a chosen amount of coffee in said cup into the coffee jug standing on the hot plate. The temperature sensor senses a "dry" condition when the reservoir has been substantially emptied, and switches off the supply of heater current to the water heater. Supply of power to the hot plate is maintained.

With the exception of said diverting- valve, the above described arrangement is conventional.

In accordance with the present invention, the machine is also equipped with a device for detecting build-up of scale. At any given time in the water heating or coffee brewing cycle, the temperature at a given point in the heater, e.g. where the temperature sensor is located, is increasingly higher with increased scale.

The scale detecting device thus comprises a timer which controls an electronic switching unit fed with the output signal of the temperature sensor (or a signal derived therefrom).

In addition, the scale detecting device comprises a comparator fed with voltage signals defining three reference level temperatures, e.g. a lower reference level of say 11 0'C, an intermediate reference level of say 1 25 C and an upper reference level of say 140"C.

The timer is activated when the machine is switched on, and a given time after the start of the heating cycle supplies the temperature sensor signal to the comparator.

Assuming the sensed temperature is not above the lower threshold, the machine is deemed acceptably free of scale and operation is allowed to continue normally.

Assuming the sensed temperature is above the lower threshold but not above the intermediate threshold, the machine is deemed partially scaled. A flashing warning light is switched on, but the coffee-making function is allowed to continue normally.

Assuming the sensed temperature is above the intermediate threshold but not above the upper threshold, the machine is deemed unacceptably scaled to the extent that damage could ensue from further usage. Thus, the water diverting valve is activated, and a continuous warning light and possibly an audible warning device are switched on. Although water heating continues, the hot water is diverted to the alternative outlet, which conveniently feeds the hot water through a filter bypass channel direct into the coffee jug. It is thus to be noted that coffee making cannot be continued with an unacceptably scaled machine.

Towards the end of the heating cycle, the temperature sensor output is switched by the - timer to be fed continuously to the comparator for monitoring purposes, and a sensed temperature above the upper threshold indicated that the reservoir is dry. The supply of current to the water heating element is therefore cut off.

The diverting valve can be a small poppet valve directly or indirectly operated by a solenoid.

It is important to appreciate the point that the water heater is not switched off when the temperature sensor indicates an unacceptabjy scaled condition. Descaling is conventional'y carried out by heating water to which a de scaling chemical, usuaily in the form of crystals, has been added. It is therefore important for de-scaling that the heater should remain operable in the presence of the scaled condition.

It will be appreciated that the particular arrangement of coffee-making machine above described may be modified in various ways within the scope of the invention as hereinbe fore defined.

Claims (7)

1. A machine having an electric water heater the temperature of which is monitored by a temperature sensor to control a heating cycle, an output derived from the sensor dur ing the course of a heating cycle is compared with at least one fixed reference level, and an electronic switch is operated to switch on an alarm device and/or to cut off the supply of heating current and/or to divert the supply of heated water is the said output is above a predetermined threshold.

2. A machine according to claim 1, wherein the temperature is sensed at a fixed time after the start of a heating cycle and, if the sensed temperature is below a first refer ence level, the cycle is deemed normal; if above a first reference level but below a second higher reference level, the heater is deemed partially scaled and a warning indica tor is activated; if above the second reference level but below a third reference level the heater is deemed scaled and the heating cycle may be interrupted or modified and/or a second alarm indicator activated.

3. A machine according to claim 2, wherein the third reference level is the tem perature sensed by continuous monitoring to wards the end of the heating cycle, the attain ment of which indicates that the heater is dry due to completion of water heating.

4. A machine according to claim 1 or claim 2 or claim 3, being a coffee-making machine having a diverting valve whereby heated water can be diverted from its normal coffee-making path, wherein a sensor output exceeding the second reference level causes activation of of the diverting valve, so that no further coffee can be made until the machine has been descaled to avoid damage which could be caused by further usage.

5. A machine according to claim 4, wherein the heater continues to be operable with the diverting valve activated.

6. A coffee-making machine having a diverting valve with when activated diverts water into an alternative path to the path through the coffee-making part (ie filter cup) of the machine and also having an electric heater associated with a sensor which monitors the temperature of the heater to control a coffee-brewing cycle, wherein a device is provided to detect scale build-up, said device comprising a timer which, at a given time after the start of a heating cycle, initiates a scale detection function, a comparator which when said detection function is intitiated receives an output derived from the temperature sensor and compares said output with at least one reference level, and circuit means for activating the diverting valve if a reference level designating a scaled up heater is exceeded.

7. A coffee-making machine substantially as hereinbefore described.