DE3101958C2 - Magnetic-inductive flow meter - Google Patents

Description

45

The invention relates to a magnetic-inductive flow meter, the magnetic coils with a Alternating current or a switched direct current are excited and its measuring electrodes each via one Preamplifier are connected to a transmitter.

In certain technical applications, for example the flow measurement of liquids with low conductivity, the requirement of long line lengths between spatially distant Transducers and transducers or in the event of large electrical interference on the measuring signal line it is common to use a preamplifier in the measuring signal lines between the transducer and the transducer provide a high input impedance for the signals coming from the electrodes and a have low output impedance in the direction of the signal cable running to the transmitter and whose auxiliary power was supplied by the transmitter via an additional cable. When used in This additional line required additional Zener barriers in potentially explosive areas.

In contrast, the invention has the task

based on enabling the power supply for the preamplifier without an additional cable.

This object is achieved according to the invention in that the excitation current line for the magnet coils an energy converter connected to the supply connections of the preamplifier is connected

With this switching arrangement, the energy for the supply of the preamplifier is taken from the excitation current obtained for the magnet coils directly in the area of the transducer, so that the previously Any additional cable provided is not applicable. Likewise, additional Zener barriers are no longer required for explosion protection. Above all is that too Installation at the measuring location is significantly simplified

If the solenoid coils are excited by alternating current or a switched direct current, a smoothing of the auxiliary power for the preamplifier can be achieved in that an energy storage device, e.g. B. is arranged in the form of a capacitor.

There are various options for converting part of the excitation current into the auxiliary energy for the preamplifier Components suitable For example, the energy converter can consist of a transformer whose primary side is the excitation current line and whose secondary side is the one with a rectifier provided supply line for the preamplifier is connected According to another version can an electro-optical converter connected to the excitation current line can be provided, the output energy of which can also act on an opto-electrical converter connected to the supply line the energy converter consist of a heating resistor connected to the excitation current line, whose Thermal energy is converted into the supply voltage by means of a thermocouple connected to the supply line. Finally, a converter circuit can also be used for energy conversion a possible loss of excitation current can be compensated by calibration

The invention is shown in the drawing, for example; it shows

F i g. 1 a magnetic-inductive flow meter in a block diagram,

F i g. 2 the subject of FIG. 1 with a transformer as an energy converter and

F i g. 3 the subject of FIG. S with a converter circuit as an energy converter.

The in F i g. 1 schematically illustrated magnetic-inductive flow meter consists essentially of a transducer and a transducer, wherein the transducer can be mounted at a location remote from the transducer. Of the The transducer is formed by a measuring tube 1 through which the measuring liquid flows, two measuring electrodes 2 arranged diametrically to one another and two magnetic coils 3, which create a magnetic field running perpendicular to the connecting axis of the measuring electrodes 2 produce. The magnet coils are connected via an excitation current line 4 to an excitation current source 5, which via a control line 6 from a Transmitter 7 is controlled. This switching arrangement can be chosen so that the excitation current is either an alternating current or a switched direct current, with the changing magnetic field however, for the tapping of the measurement signals periodically has sections in which the change over time of the

31 Ol 958

switched, the gain of the preamplifier is expediently dimensioned so that the through the Energy extraction caused a reduction in the excitation current and the resulting loss of sensitivity the measured variable is balanced. Optionally, constant current sources can also be installed in the supply lines be switched.

Other energy converters not shown in the drawing are also suitable, being in particular electro-optical or electro-thermal converters too are called. For example, an electro-optical converter, for. Legs Be connected to a light source whose radiation is transmitted by an opto-electrical converter, e.g. B. a photo diode into the supply voltage to be applied to the preamplifier 9 via the supply lines 11 is converted. A thermal conversion can, for. B. from a connected to the excitation power line 4 There is a heating resistor whose thermal energy is converted into the transfer energy by means of a thermocouple is converted. So much for a pulsating energy conversion takes place, energy stores 13 are used for smoothing

For this 1 sheet of drawings

Magnetic flux is zero or constant

The measured quantities generated by induction are

picked up by measuring electrodes 2 and queried by the transducer 7 via measuring signal lines 8 the measurement signals being passed through preamplifier 9.

The auxiliary power required for the preamplifier 9 arranged in the measuring signal lines 8 is supplied by means of an energy converter 10 from the excitation current

ίο won and the preamplifier 9 via supply lines 11 supplied as a preferred component for the energy converter 10 that shown in FIG Transformer can be selected, the secondary side of which supplies the auxiliary power Excitation of the magnet coils 3 is also a rectifier 12 and a rectifier in the supply line 11 Energy store 13 is provided in the form of a capacitor. The generated DC voltage is used Supply of the preamplifier 9.

Another embodiment is shown in FIG. 3, as provided in the device for the power converter 10 is a power converter circuit Again, an energy storage switched 13 In this embodiment the preamplifier 9 the solenoids 3 parallel

Claims (6)

31 Ol patent claims: 1. Electromagnetic flow meter, whose magnetic coils with an alternating current or a switched direct current and its measuring electrodes are connected to a preamplifier Measuring transducers are connected, characterized in that the excitation current line (4) for the solenoid coils (3) connected to the supply connections of the preamplifier (8) ner energy converter (10) is connected 2. Electromagnetic flow meter according to claim 1, characterized in that in the Supply line (11) between energy converter (10) and preamplifier (8) an energy store (13) _{] 5 is} arranged 3. Electromagnetic flow meter according to claim 1 or 2, characterized in that the Energy converter (10) consists of a transformer, on whose primary side the excitation current line (4) and on whose secondary side the one with a Rectifier (12) provided supply line (11) for the preamplifier (8) is connected 4. Electromagnetic flow meter according to claim 1 or 2, characterized in that the Energy converter (10) from an electro-optical connected to the excitation current line (4) There is a converter whose output energy is connected to a supply line (U) more optoelectric! Converter acts jo 5. Electromagnetic flow meter according to claim 1 or 2, characterized in that the The energy converter (10) consists of a heating resistor connected to the excitation current line (4), its thermal energy by means of a thermocouple connected to the supply line (11) is converted into the supply voltage. 6. Electromagnetic flow meter according to claim 1 or 2, characterized in that the Energy converter (10) consists of a converter circuit.