GB2108862A - Automatic air humidifying apparatus - Google Patents

Abstract

Automatic air humidifying apparatus in which cleaning to remove scale and other solid contaminants is initiated at variable intervals whose duration is determined as a function both of the amount of water which has been evaporated and the amount of contaminants accumulated in the cylinder. The amount of evaporated water is determined by measuring the current consumed by the electrical heating elements (2) during the operating period by means of a current/voltage converter (12) connected to the supply current which controls a VCO the output of which is counted or "integrated" by a dividing chain (16). The amount of solid contaminant accumulated is measured by determining the rate at which a fixed volume of liquid, measured by upper and lower level sensors (13, 9) within the cylinder, is discharged from the vessel through a path the flow cross-section of which is restricted by the contaminants. <IMAGE>

Description

SPECIFICATION Automatic air humidifying apparatus The invention concerns automatic air humidifying apparatus, and more particularly a technical solution for multiplying or increasing the operational reliability and service-life-time of the evaporating cylinders of such apparatus, wherein in the course of operating the evaporating cylinder cleaning or washing cycles are introduced which take into account the amount of water evaporated and the allowance of precipitated scale and other contaminants and which are effected for their intermittent removal.

The most important problem arising from operation based on the principle of evaporation by direct heating that the materials present in a dissolved or suspended state in the water that is introduced, such as scale and other contaminants, are deposited on the electrodes and internal surfaces, filters and overflow fittings of the evaporating cylinder. If there is no systematic and complete removal of these contaminants, they will form a continuous surface and gradually reduce the effective surface of the electrode as well as the effective outflow cross-section from the cylinder.

The layer of scale which has separated out and deposited cannot be removed by use of chemicals in the course of operations based on the direct heating evaporation principle. Amongst the current commercially available apparatuses only the Swedish Steamatic system employs the principle of washing the cylinder during operation, but at a relatively low efficiency. In this apparatus the beginning of the intermittent washing time can be set by means of an electro-mechanical time switch by means of which the evaporating cylinder is filled up with water introduced through a narrow cross-section inlet and then is discharged.

This solution does not employ the principle of scale removal by means of rapid temperature changes and can only remove those contaminants from the cylinder which are present therein in a dissolved state.

Its disadvantage is that during operation flakes of scales which separate out spontaneously collect in the cylinder and gradually reduce its outflow cross-section. The end of the water draining or discharge following the filling up in the washing cycle is not indicated by the lower water level sensor but rather is set by the time period for the cycle governed by the time switch. Thus it may happen for instance that if the outlet flow crosssection is reduced during the predetermined discharge time, then the evaporated cylinder is not completely drained and contaminated water is left behind. While this is repeated several times, the evaporating cylinder will contain gradually more and more concentrated dissolved contaminants and so finally it becomes inoperative.In the Steamatic system, the above-mentioned disadvantages have been sought to be overcome by making the evaporating cylinder readily dismantleable and by prescribing periodical manual cleaning cycles. The problems associated with the operation described above arise with all known apparatus employing an evaporating cylinder but with a difference that the washing cycles of the system necessitate mechanical cleaning operations at more extended intervals. It should also be mentioned that the rr schanical cleaning following break-down or the cleaning operation preceding a break-down can only be carried out when the apparatus has been shut down and the frequency of shut-down is dependent upon the hardness and the degree of contamination of the water employed in operation.

Having regard to the fact that in an apparatus of conventional operation approximately 10 litres of water are evaporated per hour, the apparatus requires several cleaning operations per week even when it uses water qualified as pure enough for drinking.

An aim of the invention is the elimination or substantial reduction of the above-mentioned disadvantages by utilising a principle of control which has not hitherto been employed in this context.

According, therefore, to the present invention there is provided an automatic air humidifying apparatus which is as claimed in the appended claims.

The invention will be described, purely by way of example, with reference to the accompanying schematic drawings, wherein: Figure 1 is a schematic diagram illustrating the principle of cleaning an evaporating cylinder according to the invention together with a block diagram of the electronic control circuitry; Figure 2 is a block diagram of the circuit arrangement for the electronic actuating operating devices in a greater detail; Figure 3 is an illustration of the operating principle of the 'digital clock' timing the washing cycles, and Figure 4 illustrates the electrical sensing of the upper and lower water level in the evaporating cylinder.

Referring to the drawings, Figure 1 illustrates an evaporating cylinder 1 having a mains circuit 11 containing an electromagnetic switch 10 and in one of the three phases of the circuit a current voltage converter 12 is connected. The task of the switch 10 is to interrupt the main circuit during the washing cycle while the voltage converter 1 2 is effective to provide operation an analog voltage signal proportional to the current supply to the cylinder which in turn is proportional to the amount of water present in the cylinder. The output signal from the converter 1 2 is used to control a voltage-controlled oscillator (hereafter: VCO) 1 5. The VCO together with a digital divider chain 1 6 constitute a digital clock which runs at a rate proportional with the amount of water supplied to the cylinder.Since the amount of contaminant such as scale, separated out from the cylinder is proportional with the amount of water fed into the cylinder, the digital clock 'resiliently' follows the amount of contaminant and initiates or triggers washing cycles at intervals proportional to the amount of water therein.

When the output of the digital divider chain 1 6 has reached a predetermined level a relay circuit 17 receives a command signal which initiates cleaning of the cylinder.

The phases of the cleaning of the cylinder are as follows: The switch 10 interrupts the mains circuit of the cylinder.

A large cross-section washing valve 4 receives a command signal. Through this a direct mains cold water stream at mains pressure and at a suitably large cross-section is passed through the electrodes and the outflow filter. Under the effect of the large and rapid change of temperature the scale that has deposited is loosened and through the mechanical energy of the water stream or jet is readily separated off. The filling with water takes place until a level set by an upper level sensor 13 is reached.

This resets the digital dividing chain 1 6 closes the large cross-section washing valve 4 and causes the relay circuit 1 7 to get a command signal for opening an electromagnetic drain valve 5 which has a diameter identical with the outflow cross-section of the evaporating cylinder 1, and a starting signal is generated for a fixed frequency oscillator 14. The frequency of the fixed frequency oscillator 14 is so chosen that in the case of a completely clean output outflow filter and outflow fittings during the drain or discharge the digital divider chain 1 6 counts to exactly one third of the above-mentioned predetermined output level of the divider chain 1 6. This value is stored by the divider chain.

The lower level sensor 9 detects the complete discharge of the cylinder and passes a command signal to the inhibiting input of the fixed frequency oscillator 14 and gives a signal for the resetting of the switch 10 via the relay circuit 1 7.

In this way the first washing cycle is terminated.

In the following evaporation cycle the digital divider chain 1 6 counts on from its condition in which it has been 'filled up' to one third.

Thereafter the period between the washing cycle is determined by the 'electrical length' of the remaining two-thirds and the frequency of the VCO 1 5 which is proportional with the amount of water.

If in the course of operating the evaporating cylinder flakes of scale are separated off, the outflow cross-section is narrowed down and during the washing cycle the evaporating cylinder can be discharged only more slowly than when it is completely clean. Thus the discharge time is increased and the fixed frequency oscillator 14 no longer 'fills up' the dividing chain to one-third but rather, proportionately with the increase, to a larger fraction. Thus, the 'division length' remaining for the subsequent evaporating cycle is shortened, that is to say the system increases the frequency or number of the washes proportionately with the increase in the scaling.

By a simple feedback of the digital dividing chain 1 6 it can be achieved that when the discharge time has increased to a predetermined value the washing cycle should be repeated several times successively until the discharge time is re-adjusted to the desired value.

Referring now to Figure 2, when the last member of the digital divider chain 1 6 counts in a BCD Code to 9 the relay circuit 1 7 receives a command signal and is energised. Thereupon the circuit of the switch 10 is interrupted.by the break contact 1 7/2 and the switch 10 is de-energised. In Figure 2, the contacts associated with relays 10, 17 and sensors 9, 13 are all shown in their deenergised positions.

The large cross-section washing valve 4 receives a command signal via the break contact 10/5 and the make contact 17/4 and thus the filling of water is initiated.

The circuit of the lower level sensor 9 is activated via closure of the break contact 1 0/1.

Since at this time there is water in the evaporating cylinder, its associated relay is energised.

When the water level reaches the upper level sensor 1 3 then the contents of the digital divider chain 1 6 are cleared via the make contact 13/1 and the relay 1 7 is de-energised.

Thus, the circuit of the large cross-section washing valve 4 is interrupted via the make contact 1 7/4 and the circuit of the electromagnetic discharge valve 5 is closed via the break contact 1 7/3 and the make contact 9/4.

The fixed frequency oscillator 14 that registers the discharge or drainage period receives a starting signal from the break contact 1 7/1 and the make contact 9/2, and when the evaporating cylinder has been completely emptied the relay of the lower level sensor unit 9 is de-energised.

In this way the circuit of the electromagnetic discharge valve 5 is interrupted via the make contact 9/4.

The electromagnetic switch 10 for interrupting the mains circuit of the evaporating cylinder is then energised via the break contacts 9/3 and 1 7/2. The control of the fixed frequency oscillator 14 is de-activated via the make contact 9/2, and the condition for the feedback to initiate repeated wash cycles, when the discharge or drainage time has increased by a predetermined amount, is interrupted via the make contact 9/1.

Thereafter a non-illustrated electromagnetic valve fills the cylinder to the operating level required for the evaporation cycle and the evaporation is initiated.

Figure 3 illustrates the current voltage converter 12, the oscillator 14 of fixed frequency for registering the period of the discharge. the VCO 15 and the digital divider chain 16 in greater detail and also illustrates their connection with each other and with the relay circuit.

The current voltage converter 1 2, the VCO 1 5 and the fixed frequency oscillator 14 are known per se from the technical literature and are arranged in accordance with the purpose. The output voltage of the converter 12 is connected to a potentiometer so as to be proportional at all times with the current flowing in the main circuit 11. The VCO connected to its output constitutes the oscillator of the digital clock that measures the cycle time of the evaporation cycle. Its frequency is at all times proportional to the amount of water present in the evaporating cylinder 1 by virtue of the linear interrelation between the water present in the evaporating cylinder 1 and the amount of current received by the evaporating cylinder.

The amount of scale and other contaminants that separate out in the course of operation in the evaporating cylinder is exactly proportional with the amount of water and thus the digital clock made up of the VCO 1 5 and the divider chain 1 6 introduces washing cycles into the operation of the cylinder, in the same ratio. The output of the VCO is connected via an OR-gate 29 to the input of a divider chain 28 having a division ratio of 1 06.

An AND-gate 30 is connected to the other input of the OR-gate 29. The fixed frequency oscillator 14 for registering the time period of the discharge is received via the AND-gate 30 at the input of the dividing chain only when the output of the Schmitt-trigger 31 is at level H ("1). The Schmitttrigger 31 is switched to level H through smoothing RC elements only during the discharge period, that is to say, only when the break contact 1 7/1 and the make contact 9/2 are both closed.

The dividing ratio of the dividing chain 28 and 32 is 9.106 which count must be reached in order to initiate the washing cycle. When this number of impulses have arrived at the input the decade divider 32 counts exactly to nine. The QA output 20 and QD output 21 are switched to a high level and via the AND-gate 22 connected to these outputs as well as via a transistor 25, the relay 17 receives a command for initiating the washing cycle and thus the water-filling into the cylinder is started. When the water level has reached the electrode of the upper level sensor 13, then the content of the dividing chain is cieared via make contact 13/1 and the RC elements and the Schmitt-trigger 27. The relay circuit 1 7 is deactivated but the lower level sensor 9 remains activated.

Through the break contact 1 7/1 and 9/2 the condition for connecting the signals of the fixed frequency oscillator 14 which registers the drainage time is then realised.

The frequency of the oscillator is such that when the outflow cross-section of the evaporating cylinder is completely clean the drainage time has a length which corresponds to counting by the digital divider chain 1 6 to one third of its range, i.e. to 3 x 106. The chain then preserves this value and in the next evaporating cycle a fresh wash is initiated when the dividing chain counts a further 6 x 106 impulses from the output of the VCO 1 5 and the content of the counter 32 is nine.

If scaling arises in the cylinder the outflow cross-section is decreased and the discharge time is increased. The number of seconds by which the drainage time increases causes a decrease in the number of seconds of the evaporating cycle before the next washing cycle multiplied by the ratio of frequencies of the oscillators 1 4 and 1 5.

The feedback based on the AND-gates 23 and 24, the Schmitt-trigger 26 and the operating contact 9/1 always initiates repeated washing cycles when the original discharge time is doubled, i.e. when the content of the decade divider 32 becomes six during the drainage or discharge. When the QD output 1 8 and QC output 1 9 are switched to a high level, a high level pulse is passed to the input of the decade divider 32 which sets it to 9. Then the decade divider 32 initiates a repeated washing cycle and this is repeated as many times as is necessary until the cylinder is decontaminated to the extent of being able to discharge in a time shorter than double the original discharge time.

Figure 4 illustrates the level detectors of the evaporating cylinder during washing. The upper level detector 1 3 has an electrode which is originally part of the evaporating cylinder while the level detection at the lower level takes place in a metallic tube 6 disposed next to the cylinder and connected to the cylinder on the principle of communicating vessels. To enable the tube 6 to be closed at the top it is connected with the steam outlet of the cylinder via a tube section 33.

During evaporation the water is usually heated by the ohmic resistance of the water in the cylinder. In the washing cycle the conductivity of the water is again utilized for level detection. The water present in the shut down cylinder is always set to zero potential via the outflow fittings of the pipe 6. The rectifiers of the lower sensor are connected between the phase line 11 and the electrode. After suitable filtering the output of the rectifiers is fed to low current relays dimensioned to the phase voltage.

The automatic cleaning apparatus according to the invention considerably reduces or eliminates the disadvantages of apparatuses known hitherto.

It is made up of modern electronic elements, requires little or no maintenance and monitoring and does not need expensive replacement of the evaporating cylinder.

To illustrate the increase of the service life of a cylinder that can be attained, in operational conditions where hitherto a manual cleaning was required every two days and every two weeks the cylinder had to be replaced, the evaporating cylinder could be operated for a whole year without manual intervention. The automatic control according to the invention can be fitted on a single board of 100 x 1 50 mm while its relay circuits can be mounted in a box of 200 x 70 x 50 mm. Its production costs do not exceed the purchase costs of a single evaporating cylinder. The automatic system can be readily adapted to already existing operating systems.

Claims (14)

1. Automatic air humidifying apparatus, wherein for cleaning the interior of the evaporating cylinder there is a large cross-section washing valve on the upper part of the evaporating cylinder, a cold water pipe connected to the valve, upper and lower water level sensors, a voltage converter connected to one phase of the main circuit, a voltage control oscillator connected to the converter, a digital divider chain connected in series after the voltage control oscillator, a relay circuit and the digital dividing chain and the upper level sensor as well as a fixed frequency oscillator are connected with the lower level sensor.

2. Apparatus according to claim 1, wherein the electrode of the lower level sensor is disposed in a tube connected in parallel with the evaporating cylinder.

3. Apparatus for controlling the intermittent cleaning of a liquid heating cylinder or like vessel to remove solid contaminants therefrom accumulated after variable periods of operation during which liquid is heated in the vessel, the apparatus including means for determining the duration of each of said variable periods as a function both of the volume of liquid which has been heated in the vessel during that period and of the amount of solid contaminants accumulated in the vessel.

4. Apparatus as claimed in Claim 3, wherein the volume of water heated in the vessel during said variable period is determined by measuring the current consumed by electrical heating elements within the vessel.

5. Apparatus as claimed in Claim 4, including means for counting or integrating the output of a voltage controlled oscillator controlled by a voltage representative of the current consumed by the heating elements to provide a measure of the volume of liquid heated in the heating vessels.

6. Apparatus as claimed in any one of Claims 3 to 5, wherein the amount of solid contaminants accumulated within the cylinder is determined by measuring the rate at which liquid discharges from the vessel through a discharge path the flow cross-section of which is restricted by said contaminants.

7. Apparatus as claimed in Claim 6, including means for counting or integrating the output of a fixed frequency clock or oscillator during the time taken for a fixed volume of liquid to discharge from the vessel through said discharge path.

8. Apparatus as claimed in Claim 6 when dependent upon Claim 5, wherein the same integrating or counting means is used to count or integrate the output of said VCO and said fixed frequency oscillator or clock, cleaning of the vessel being automatically initiated when the output of the counting or integrating means reaches a predetermined value during an operating period starting at a value determined by measuring the rate of discharge of liquid from the vessel immediately prior to that operating period.

9. Apparatus according to any one of Claims 6 to 8, wherein cleaning of the cylinder is repeated whenever the rate of discharge of liquid from the vessel through said path is below a predetermined value.

10. Apparatus according to any one of Claims 3 to 9, wherein cleaning of the vessel comprises subjectiny the interior of the vessel to a rapid change in temperature.

11. Automatic air humidifier apparatus including apparatus as claimed in any one of Claims 3 to 10.

12. Automatic air humidifying apparatus substantially as shown in and as hereinbefore described with reference to the accompanying drawings.

13. A method of controlling the intermittent cleaning of a liquid heating cylinder or like vessel to remove solid contaminants therefrom accumulated after variable periods of operation during which liquid is heated in the vessel wherein the duration of each said variable period is determined as a function both of the volume of liquid which has been heated in the vessel during that period and of the amount of solid contaminants accumulated in the vessel.

14. A method according to Claim 13 substantially as shown in and as hereinbefore described with reference to the accompanying drawings.