DE29723390U1 - Level monitoring device in a heated bath vessel, especially a laboratory thermostat - Google Patents

Description

PATENT ATTORNEYS · EUROPEAN PATENT ATTORNEYS · j J

Dannenberg · Schubert"·'GUdeL'

ASSOCIATED WITH KÜHNEN ■ WACKER & PARTNER GROSSE ESCHENHEIMER STRASSE 39, D-60313 FRANKFURT

· I

KWP

Patent attorneys

GERDA DANNENBERG

PA, EP, Dipl.-Ing.

SIEGMAR SCHUBERT

PA, EP, Dipl.-Ing.

DIETHER GUDEL

PA, EP, Dr. phil.

Telephone: 069-287274 Telephone: 069-287464 Fax: 069-287242

FRANKFURT

June 4, 1998
SS/Sm

Lauda Dr. R. Wobser GmbH & Co. KG Pfarrstrasse 41/43 97912 Lauda-Königshofen DE

RAINER A. KÜHNEN PA, EP, Dipl.-Ing.

PAUL A. WACKER

PA, EP, Dipl.-Ing. Dipl.-Wirtsch.-Ing.

DR. PETER WEINHOLD

PA, EP, Dr. rar. nat Dipl.-Chem.

DR. PETER FÜRNISS PA EP, Dr. rar. nat. Dipl.-Chem.

FERDINAND A. BRANDL

PA, EP, Dipl.-Phys.

HELMUT HÜBNER

PA, EP, Dipl.-Ing.

KONRAD T.WINTER

PA. EP, Dipl.-Ing.

DR. WALTER ROSS

PA, EP, Dr.-Ing. Dipl.-Ing.

DR. JÜRGEN KAISER

PA, EP, Dr. rer. nat. Dipl.-Chem.

DR. WILLI POLTE

PA, EP, Dr.-Ing. nat. Dipl.-Ing.

BERND HENNINGER

PA, Dipl.-Ing.

DR. JOERG DORNER

PA, EP, Dr.-Ing. Dipl.-Ing.

PETER KINDERMANN

PA, EP, Dipl.-Ing.

DR. DYDRA KUHLEN

PA, ER Dr.-Jur.

DR. WOLFGANG RITTHALER

PA, EP, Dr. rer. nat. Dipl.-Chem.

FREISING

Level monitoring device

in a heated bath vessel, especially a laboratory thermostat Bank details:

Dresdner Bank Frankfurt

04 704150 00 (bank code 50080000)

Postbank Frankfurt 112951-601 (bank code 50010060)

VAT number: DE 812127333

Device for monitoring the level in a heated bath vessel, in particular a laboratory thermostat

The invention relates to a device for level monitoring in a heated bath vessel, in particular a laboratory thermostat according to the preamble of claim 1.

With such known level monitoring devices, a tempering liquid in the heated bath vessel is to be protected against overheating if the tempering liquid in the bath vessel is too low. Such overheating is particularly dangerous if a flammable liquid is used as the tempering liquid, which can ignite on a part heated by the heater.

Therefore, known devices for level monitoring in a heated bath vessel of the type mentioned above serve to prevent the heating element from being switched on if the level of the bath fluid is too low or, if it is already switched on, to switch it off.

In this context, laboratory liquid thermostats suitable for use with flammable liquids are provided with floats or other monitoring devices such as pressure sensors for detecting the static liquid pressure as essential parts of such monitoring devices. In particular, a known laboratory thermostat of the type mentioned above is provided with a float that protrudes downwards from a housing of the thermostat and can be inserted into a bath vessel together with a circulation pump and a heating device arranged underneath it (DE 195 19 809 Al). However, such a level monitoring device is technically complex if it is to work reliably. In addition, such level monitoring devices tend to be susceptible to failure, especially if they are used under difficult operating conditions in a

should work over a very wide temperature range.

A magnetic float with the disadvantages described is also used in DE-GM 7 316 083. This deals with a thermostat and, among other things, with switching its heating on and off when the liquid level drops. As an alternative to an encapsulated magnetic float on the outlet side of the pump, an encapsulated thermostat is used to determine a reduced pressure at the pump outlet in order to detect a liquid level that is too low, whereupon the electrical supply to the pump motor, the heating elements and the cooling group is switched off. The disadvantages of these solutions (need for a breaker or additional relay) are pointed out in this document. Furthermore, both alternative detection devices must be provided directly in the bath vessel or directly on the pump outlet side.

Other conceivable level monitoring devices with sensors that work with ultrasound or microwaves and can directly monitor the liquid level with corresponding transmitters and receivers require complicated, technically complex electronic components.

The present invention is therefore based on the object of developing a device for level monitoring in a heated bath vessel, in particular a laboratory thermostat, of the type mentioned at the beginning, in such a way that the level of a tempering liquid in the bath vessel can be reliably detected using technically uncomplicated but precisely operating means in order to not switch the heating element on or to switch it off if a predetermined level is undershot.

This object is achieved by designing the device of the type mentioned at the outset for level monitoring with the features specified in the characterizing part of claim 1.

The solution principle is based on using the circulation pump, which is already provided for circulating the tempering liquid, and the electric motor that drives it, as well as the associated hardware components of the actual performance parameter recording and control, which are typical of a pump system, in particular of laboratory thermostats, as an aid for level monitoring. This is based on the knowledge that when the circulation pump is arranged with an intake opening above the radiator, the performance parameters of the electric motor can be used as an auxiliary variable for recording the level. The speed of the circulation pump or the electric motor can serve as a performance parameter that is to be recorded using sensor means if the electric motor consumes a constant electrical power that is essentially independent of the load. In this case, the speed is the actual motor performance parameter, which is recorded using the sensor means and compared with a target motor performance parameter in a target motor performance parameter range. The speed is one factor of a product, the second factor of which is the torque of the electric motor, in this case a mechanical power that is in a largely constant ratio to the regulated electrical power. If the level of the tempering liquid is too low and the circulation pump is running practically empty, the torque with which the electric motor is loaded by the circulation pump drops, so that with a constant power consumption of the electric motor, the speed increases accordingly. The increased speed is therefore a measure of the level being undershot. The solution alternative according to claim 2 is based on this.

However, it is also possible to use electrical power recording devices as sensor means to evaluate the electrical power consumed by the electric motor for level monitoring, where the speed of the electric motor is regulated to a constant value. In the case where the circulation pump is not immersed in the tempering liquid, the electrical power is significantly low, corresponding to the low

lower torque that the electric motor has to deliver to the circulation pump in this operating case. This alternative solution is the subject of claim 4.

A speed measurement has already been proposed as an alternative measure for monitoring the flow rate of a pump system (US 5,601,413), but this does not suggest the solution principle according to the invention for the following reasons. US 5,601,413 deals with a pump system, e.g. for chemical liquids from a container. It is about determining the amount of liquid pumped from a flow rate determined using additional sensors. It is stated that the usual measures of measuring the pump speed to determine the flow rate and using level sensors disadvantageously require additional sensors in the liquid container. It is therefore proposed in this US patent to determine, for example, a drop in level and emptying of the container by the change in the flow rate that occurs as a result of the associated air intake. For this purpose, in the exemplary embodiment, a flow meter is connected to the pump outlet. Although the possibility of recording the speed of the pump as an alternative to flow rate monitoring is mentioned, this, however, as already explained, disadvantageously requires the installation of further sensors, which is precisely what this US patent is intended to avoid.

In contrast, the present invention is characterized above all by the fact that it uses existing components of the circulation pump system for level monitoring and thereby advantageously utilizes control means already provided for the electric motor.

In both alternatives according to the invention, the device for level monitoring is completed by a comparison device which is suitable for comparing the said actual engine performance parameter with a target engine performance parameter range

and to issue a monitoring signal including the under-level signal if the actual engine performance parameter is outside the target engine performance parameter range.

The target engine performance parameter range is defined by tolerance field values which are expediently stored in a memory of a computer which, according to claim 5, also implements the comparison device.

If the speed is to be measured, the tolerance field values are assigned to the set motor power. For this purpose, adjustment means for the power consumption of the electric motor are coupled with adjustment means for the target motor power parameter range, i.e. the tolerance field values in the comparison device according to claim 3.

The feature of the invention that a monitoring signal is emitted by the comparison device when the actual motor performance parameter is outside the target motor performance parameter range not only includes detection of the temperature control liquid falling below a specified level, but also the operating case in which the pump is not running or is running only slowly, so that sufficient circulation of the temperature control liquid cannot occur. In this case, the speed of the electric motor detected according to the first alternative is too low, while in the case of detecting the electrical power with corresponding power detection means when the speed of the electric motor is controlled, the electrical power can be too high, namely if the pump is blocked. If the power supply to the electric motor is interrupted, the electrical power detected in the second alternative is too low despite the speed control. In all of the above cases, a monitoring signal is generated, which can serve as an actuation signal for a switch with which the power supply to the heating element is interrupted for safety reasons. This results in the additional

6 '

Advantage that the heating is only switched on when the pump speed is within a tolerance range that is not reached by level monitoring with a separate device provided for this purpose without a self-test.

An embodiment of the invention is explained below using a drawing with two figures:

In Fig. 1, a laboratory thermostat is shown roughly schematically from the side, partially cut away, in which the speed of the motor or pump is evaluated for level monitoring when the power of the motor or pump is regulated independently of the load, and in Fig. 2, motor performance parameters in switch-on ranges for different pump performance levels are shown in a diagram.

In Fig. 1, 1 indicates a bath vessel of a laboratory thermostat, above which its housing 2 is located. A connecting pipe 3 protrudes downwards from the housing to a circulation pump 4, which is intended as an immersion centrifugal pump for circulating a tempering liquid 5. For this purpose, the circulation pump 4 is connected by a shaft (not shown) to an electric motor 6 as a pump motor in the housing 2. A pump housing 7 has an intake port 8 with an intake opening 9 in the middle at the bottom. On the side of the pump housing

7 an outlet opening 10 can be seen, from which a connection piece 11 for an external heat exchanger (not shown) protrudes upwards.

Completely below the intake opening 9 of the intake manifold

8, a heated part 12 with a heating element 13 is arranged. The heating element 13 is in a circuit with a controllable switch 14 in the housing 2 and power supply terminals 15, 16.

The controllable switch 14 is preferably two-pole. It is actuated by a comparison device with memory 17, which emits a monitoring signal via a connection 18.

The comparison device receives input signals via a connection 19 from a speed detection means 20 coupled to the electric motor 6, which can be designed with a Hall sensor as a magnetic sensor with a sensor disk rotating with the electric motor. The Hall sensor can be provided anyway for detecting the position of the motor as a component of the pump system. The comparison device is connected to a setting means 22 of the target motor performance parameter range via a second input-side connection 21.

The setting means of the target motor power parameter range activates tolerance field values stored in the comparison device with memory for the target speed of the electric motor 6 according to a setting of a setting means 23 of the power consumption of the electric motor, which acts on an electrical power regulator 24.

The supply of activatable tolerance values, which are stored in the comparison device with memory 17, is also referred to in the present documents as the target engine performance parameter range. Such ranges - referred to there as switch-on ranges - are shown in Fig. 2. They include speed values as engine performance parameters, which can occur when a pump performance level is switched on (essentially proportional to the engine performance level). The pump performance levels 1 to 5, one of which can be set, are shown as the ordinate.

The comparison device with memory 17 works independently of a temperature control (not shown) by comparing the speed of the electric motor 6 detected by the speed detection means 20 with the selected tolerance field values.

which are assigned to the set motor power. When the tolerance field values are exceeded or undershot, the controllable switch 14 to the heating element 13 is opened via the connection 18 by a monitoring signal generated in the comparison device 17, so that the heated part 12 cannot overheat. To ensure this, the heating element 13 with the heated part 12 is arranged in such a way that the heated part 12 is located below the intake opening 9 in the intake port 8 of the pump.

Claims (1)

Protection claims: 1. Device for level monitoring in a heated bath vessel, in particular a laboratory thermostat, with sensor means, with a circulation pump in the bath vessel driven by an electric motor, which is in fluid-conducting connection with the interior of the bath vessel via an intake opening, and with a part heated by a heating element, which is arranged in the bath vessel below the intake opening of the circulation pump, the heating element being in an electrical heating circuit which can be switched on and off depending on a signal emitted by the sensor means that the level is below the limit. characterized, that the sensor means in the control device (20, 22, 23, 24) of the motor (6) are sensor means (20) for detecting at least one actual motor performance parameter, which are connected to the electric motor (6), that the sensor means are connected on the output side to a comparison device with memory (17) for comparing the actual motor performance parameter with a target motor performance parameter range and for emitting a monitoring signal
including the under-level signal when the actual engine performance parameter is outside the target engine performance parameter range. . Device according to claim 1 with an electric motor which absorbs a constant electrical power which is essentially independent of the load,
marked by Speed detection means (2) as the sensor means for the level monitoring and engine control. 3. Device according to claim 2 with means for adjusting the electrical power consumption of the electric motor in its control device, characterized,
that the adjustment means (23) of the power consumption of the electric motor (6) are coupled to adjustment means (22) of the desired motor power parameter range in the comparison device (17). 4. Device according to claim 1 with a speed control of the electric motor in its control device,
characterized, that electrical power detection means are electrically connected to the electric motor as sensor means for level monitoring. 5. Device according to one of the preceding claims,
characterized, that the comparison device (17) is part of a computer in which tolerance field values, the stock of which corresponds to the target engine performance parameter range, are stored.