DE2429482C3 - Device for measuring and / or monitoring temperatures, levels and / or flow conditions of electrically conductive liquids of high specific heat - Google Patents

Description

The invention relates to a device for measuring and / or monitoring temperatures and levels and / or flow states of electrically conductive liquids of high specific heat, in particular by Wass <*. which as a sensor a temperature-dependent Has a resistance with clamp contact, which is used for insulation with a shrink tube is wrapped

From DE-OS 21 07 365 a shrink tubing is covered PTC thermistor combination with terminal contact for the demagnetization of color television sets known. Such a structure is not suitable for Use in electrically conductive liquids with high specific heat, as the casing is on one side is open and since, on the other hand, the PTC thermistors are only contacted at very small areas As a result, the heat transfer from the contact electrode to the PTC thermistor is very low, which is a results in a large time constant for the combination. Time constant here is the time understood that the PTC thermistor needs until its temperature is adapted to that of the environment

Furthermore, from the "Siemens magazine" 1969, issue 4, p. 392 to 394, and issue 9, p. 793 to 7%, PTC thermistors Known with shrink tubing The known ones PTC thermistors are used for temperature monitoring and excess temperature protection for those at risk of temperature Machines and devices, in particular electric motors. The well-known PTC thermistors covered with shrink tubing have soldered connection wires and have plastic insulation. They are not suitable for Use in liquids with high specific heat, as the temperature shock occurs when the probe is immersed it is strong that after a few measuring cycles the soldering points can become detached.

The object of the invention is to provide a device for measuring and / or monitoring temperatures, Indicate level heights and / or flow states of electrically conductive liquids with which the difficulties listed above can be circumvented.

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In the device described at the outset, this is achieved according to the invention in that the contact electrodes consist of resilient sheet metal strips, one end of which with the end of a power supply serving wire is soldered, and which spiral around this end of the braid are wound, and that the open end of the shrink tube with a Plastic drop is closed

As a temperature-dependent resistor, either a thermistor or a PTC thermistor can be used.

The advantages of the invention are based on the drawing, which shows an embodiment of the invention Device shows shown in the accompanying figures shows

Fig. 1 is a longitudinal section through the inventive Device and

FIG. 2 shows a cross section along the plane H-II of FIG. 1.

In the F i g. 1 and 2 is a PTC thermistor disk with 11 denotes, which has a barrier layer-free metal coating 12 The connecting strands! 3 are at their upper Stripped end; a sheet metal strip 14 is soldered to this upper end and spiraled around the Wrapped around the end The material for the sheet metal strip 14 is preferably tinned bronze foil 0.2 mm thick is used

The spirally wound sheet metal strips 14 are by means of serving as a sheath and insulation shrink tubing 15 against the metallized PTC thermistor surfaces pressed. The spring action of the sheet metal strips creates one that occurs in all Operating conditions safe contact, which is particularly due to the temperature shock when immersed in the liquid of high specific heat cannot be destroyed. On the other hand, the Spirally wound sheet metal strips 24 a good heat transfer due to its large contact points, so that the device has a low rate constant

In order to produce the tightness required for level sensing and measurement, the open The end of the shrink tube 15 is closed by means of a plastic drop: 16.

During operation, the PTC thermistor is brought into the temperature range of the steep by an applied measuring voltage Resistance increase heated with this operating state in the area in the current-voltage diagram falling Siirom voltage characteristic curve is Da in Liquid can dissipate more heat, the PTC thermistor is at a lower level Temperature than in air, d. H. it has a lower resistance value in liquid. This results in a higher current through the PTC thermistor when it is in liquid

In one embodiment of the device according to the invention, a PTC thermistor of the nominal temperature was used (Start of the increase in resistance) of 80 ° C is used, which has a resistance value at 25 ° C of 60 ohms. In this embodiment, an applied voltage of 20 V resulted in air Current values of around IO mA and in water around 50 mA.

For other liquids, different but similar values result depending on the thermal resistance.

Circuits in which the device according to the invention can be used are, for. B. in DE-PS 15 73 085, which has an electronic thermistor compensation

tion circuit for overfill protection of liquid tanks concerns, and in DE-PS 15 73 090, which a Process and a circuit arrangement for securing liquid tanks against overfilling concerns, described.

1 sheet of drawings

Claims (2)

Patent claims: 1. Device for measuring and / or monitoring temperatures, levels and / or Flow states of electrically conductive liquids of high specific heat, in particular of Water, which as a sensor has a temperature-dependent resistance with terminal contact which is covered with a shrink tube for insulation is characterized in that the contact electrodes consist of resilient sheet metal pieces (14), one end of which with the end of a as a power supply serving braid (15) is soldered and which spiral around this end of the braid are wound up and that the open end of the shrink tube (15) with a plastic drop (16) is closed 2. Apparatus according to claim 1, characterized that the resilient sheet metal strips (14) consist of tinned bronze foil.