DE10028448A1 - Galvanically-separated current sensor for circuit monitoring and control applications, includes inverted U-shaped conductors wound over toroidal core and soldered to conductor strips on PCB - Google Patents

Abstract

A toroidal core (1) with a Hall element (3) at its air gap (2), is soldered to a PCB (7). The open ends of the inverted U-shaped conductors (6) wound around the core, are soldered to the conductor strips (8) on the PCB. A digital or analog signal processor on the PCB or Hall-element provides temperature compensation for the output of the Hall element depending on the ohmic offset voltage of the element, temperature coefficient and temperature-dependent amplification of the Hall element at 20 deg C, current to be measured and the supply current, circuit constant such as air gap length.

Description

The invention relates to a. Device for galvanic ge separated measurement of an electri flowing in a conductor current using one of the conductors in several Coils wrapped on a printed circuit board applied toroid with an air gap, in which a linear, attached to the printed circuit board and there electrically connected Hall element is also introduced, whose output voltage is proportional to the magnetic flux density of the current to be measured and in the toroid bundled magnetic field.

There are a variety of applications in which an electri shear current is to be measured. The measured value is z. B. for monitoring required or for regulatory purposes. In the simplest case, he follows the current measurement with a measuring resistor. It leaves one measures the current I to be measured by a known ohmic Resistor R, the measuring resistor, flows. The above the Meßwi the level R applied voltage U is then a measure of the Strength of the current I. The basis here is the ohmic Ge set: R = U / I or U = R.I.

However, there are some applications where the electricity measurement is galvanically isolated, so it is done without contact should. You get a potential-free and therefore also low-interference measurement.

In principle, the problem of galvanically isolated current measurement has been solved for a long time. B. to the book "Elektromeßtechnik", Siemens AG, Munich and Berlin, 1968, 5th edition, page 34, in particular Fig. 10 and its description. Then a Hall generator is arranged in the air gap of an iron core surrounding a current-carrying conductor. The Hall voltage proportional to the magnetic field in the air gap and thus the current in the conductor is measured with a suitably calibrated moving coil instrument. The measuring circuit is thus galvanically isolated from the "main circuit".

With the galvanically isolated measurement of the current it is be knows to use the so-called compensation principle. In In this context, the Technical Information of the LEM, CH-1228 Plan-les-Ouates, "Electronic components ten, New generation of ASIC compensation current transformers up to 25 A ", publication CH 98102 D 03.98 5 CDH.

Corresponding to the mode of operation described there and explained with reference to Figure 1 of the publication mentioned, here generates a magnetic field for each conductor through which a current flows, which is amplified in a magnetic circuit. This field can be measured in an air gap. A Hall element is used for this. When supplied with a constant current, this has the property of converting the magnetic flux into a voltage. With the compensation principle, the voltage is only used to regulate the balance between primary and secondary flow. About an additional, secondary compensation winding with z. B. 2000 turns, a 1/2000 of the primary current flows to exactly compensate for the field of the primary conductor. The total flow is then zero. The control works with direct current and with alternating currents up to the limit frequency of the electronics. In addition, the current transformer works like a normal transformer with primary and secondary windings. In this way, currents up to several 100 kHz can be measured potential-free.

Figure 2 of the cited document shows in a photo the external design of the LEM current sensor, the dimensions (length × width × height) of 9.3 × 22.2 × 24 mm specified in table 1 1, despite the compact design for many people turns are still too big.

Working according to the compensation converter principle Current measuring devices are therefore for many areas of application still too big. In addition, their bandwidth is around 100 kHz limited. In addition, they adversely point inherently a delay time between on and off going on.

In the galvanically isolated measurement of the current, the version with a linear Hall element is also known, to which be already known at the beginning in connection with the known from the book "Elektromeßtechnik", Siemens AG, Munich and Berlin, 1968, 5th edition, page 34 the technique has been received and that the reference to FIG. 1 and FIG. 2 be below is written.

In this case, a slotted toroidal core 1 is used, similarly to the so-called compensation converter described above. In the air gap 2 of the toroidal core 1 , a linear Hall element 3 is introduced, the output voltage is proportional to the magnetic flux density B. The magnetic field generated by the current I _mess to be measured is bundled in the toroidal core 1 and converted by the Hall element 3 into an electrical output voltage, the so-called Hall voltage. The relationship between the flux density B and the current I _mess to be measured results in:

where B is the magnetic flux density, I _meas the current to be measured, N the number of turns around the toroid 1 , µ ₀ the magnetic field constant and l _L the length of the air gap 2 .

Fig. 1 shows in which a conductor 4 performed through the opening of the toroidal core 1 an embodiment. The conductor 4 carries the current I _mess to be measured by means of the Hall element 3 . Fig. 2 shows, on the other hand, an embodiment in which the conductor carrying the current to be measured is wound in several (N) turns 5 around the toroidal core 1 for measuring smaller currents. Such devices are described in DE 39 05 060 A1, among others.

The _following results for the output voltage U _{HALL of} the _Hall element 3 :

U _HALL = K (T) .I _V .B,

where U _{HALL is} the Hall voltage, K (T) is the temperature-dependent gain of the Hall element, B is the magnetic flux density and I _{V is} the supply _{current of} the Hall element.

Current sensors with a linear Hall element can be made more compact build as a compensation converter and their bandwidth is high ago. However, this is for the purpose of measuring small currents (generally less than 10 A to 20 A) existing requirement  the winding of the toroidal core considerable manufacturing technical disadvantages. So it happens very often that the ring core provided with an air gap breaks during winding. The Contacting the live connections is also possible not completely unproblematic. A certain disadvantage of Current measuring devices with a linear Hall element compared to the that according to the principle of compensation consists in something higher temperature dependency since the Hall element is not only at magnetic field densities close to zero. The reinforcement edges tion is therefore included in the measurement result.

The object of the invention is to build a very compact Current sensor with galvanically decoupled current measurement and ho to create bandwidth that is technically feasible Lich the winding of the toroid and the contacting of the current-carrying connections can be easily implemented and oh Difficulties with temperature compensation can be provided.

According to the invention, which relates to a device of a gangs mentioned type, this task is ge that triggers the turns of the conductor from U-shaped, the ring core each encompassing conductor brackets and on the printed Circuit board matching tracks arranged together are set with the open ends of the U-shaped conductor stirrups with the ends of the respectively assigned conductor tracks me are connected mechanically and electrically in such a way that an electrical inference of the U-shaped conductor bracket and thus a behavior from the Conductor tracks and the U-shaped conductor bracket formed Kom combination corresponding to a wire wound around the toroid results. The device designed according to the invention  for galvanically isolated current measurement is considerable simpler and more compact than the previously implemented solutions.

An advantageous embodiment of a device according to the invention is characterized in that the flat plate trained Hall element standing vertically in the printed circuit board to the appropriate there ordered connection points is soldered that the toroid the printed circuit board and ge to the Hall element is stuck and that the U-shaped encompassing the toroid The ends of the conductors in the printed circuit board tine at two connection points at the ends of two assigned conductor tracks are soldered. The assembly of a device designed in this way is carried out in an expedient manner in a sequence of steps following the order of the above given characteristics.

The device according to the invention or the Hall element contained in this, however, have in principle a compensation dependency which is not inconsiderable without additional compensation measures, which is explained below. The output voltage U _HALL (T) of the _Hall element and its dependence on the temperature can be described as follows:

U _HALL (T) = U _HALL0 (T) + K (T) .k _geom .I _mess .I _V

Here is
U _HALL0 (T) = U _HALL0 . (1 + TC _VR10 .dT) the temperature-dependent ohmic offset voltage of the _Hall element with the offset voltage U _{HALL0 of} the _Hall element at 20 ° C and the temperature coefficient that can be determined from data sheets or by measurement TC _VR10 the offset voltage,
K (T) = K0. (1 + TC _V20 ) the temperature-dependent gain of the Hall element with the gain K0 at 20 ° C and the temperature coefficient TC _{V20 of} the gain, which can be determined from data sheets or by measurement.
k _{geom is} a constant resulting from the structure (air gap _length , etc.),
I _measured the current to be measured, and
I _V the supply current of the Hall element.

It can be seen from the above equation that both the ohmic offset voltage as well as the gain of the Hallele are temperature-dependent. With a temperature change from 100 ° C errors occur in the double-digit percentage range reach into it. These are deviations for control tasks usually intolerable.

According to an advantageous development of the invention, measures for temperature compensation are therefore provided such that the output voltage of the Hall element is directly proportional to the current to be measured, regardless of the temperature. An expedient possibility in this connection is that the temperature-dependent output voltage is used for temperature compensation

U _HALL (T) = U _HALL0 (T) + K (T) .k _geom .I _mess .I _V

of the Hall element at a constant supply current I _V, the supply voltage U _V applied to the Hall element is measured as a measure of the temperature of the Hall element and the offset voltage of the Hall element is calculated therefrom and this is first subtracted from the measured output voltage U _HALL (T) of the _Hall element, so that there is an offset-corrected output voltage

U _HALL (T) off_korr = K (T) .k _geom .I _mess .I _V

of the Hall element, and that the correction of the amplification takes place either by varying the supply current I _V or by dividing the offset-corrected output voltage U _HALL (T) off_korr of the Hall element by (1 + TC _V 20), so that as a result a temperature-compensated Output voltage

U _HALL = K0.k _geom .I _mess .I _V = const..I _mess

of the Hall element is obtained.

Such temperature compensation can be advantageous run in the form of an analog circuit, but can also in In the form of a digital processing unit, which does the necessary calculations. The ana Loge circuit or digital processing unit can the printed circuit board on which the ring is located core and the Hall element are arranged.

Devices for temperature compensation in current measuring equipment lines with Hall element are known. In this context reference is made to DE 195 44 863 A1, from which it is known compensation of the sensitivity temperature response by achieving that with a compensation circuit the temperature-dependent change in the internal resistance of the Hall elements a positive temperature coefficient of the tax Stromes is formed, which is dimensioned so that it the negative  Temperature coefficients which determine the sensitivity compensating other physical quantities.

A similar temperature compensation is known from DE 32 17 441 A1 de arrangement known with a Hall element, in which the tem temperature-dependent offset voltage of the Hall element will. The compensation is carried out by regulation the output voltage of the Hall element as a function of ei nem signal that is typical of the impedance which of the Arrangement for that supplied by a constant current source Supply current of the Hall element is given. The governing Signal is a signal that corresponds to the voltage drop who speaks across the arrangement by the constant Supply current of the Hall element is generated.

The invention is based on the attached drawing explained. Show it:

Fig. 1 is a perspective view of a known electrically isolated Stommeßeinrichtung linear Hall element using a toroidal core through which the conductor is guided stromfüh Rende introduction already described,

Fig. 2, the introduction also been described by-perspective view of a known electrically isolated means for measuring small currents with linear Hall element using a toroidal core, around which the current-carrying conductor is wound containing more reren turns,

Fig. 3 is a perspective view of an exploded illustration of the invention, accordingly the structural design embodied means for measuring the current with the Hall element,

Fig. 4 is a perspective view of the mounting of the Hall element on a printed circuit board,

Fig subsequent assembly of the ring core board. 5 in a perspective view on the printed circuit,

Fig. 6 also in a perspective view of the constructive complete construction of a device according to the invention after complete assembly, and

Fig. 7 shows the equivalent circuit of a Hall element.

Fig. 3 shows a perspective view of the exploded view of the construction of a current measuring device designed according to the invention. The latter consists of a slotted ring core 1 , which has an air gap 2 and is generally a base body made of soft iron, a linear Hall element 3 , electrically conductive U-shaped conductor 6 and a printed circuit board 7 , which may contain additional circuitry. On the printed circuit board 7 there are conductor tracks 8 which provide the electrical inference of the U-shaped conductor bracket 6 . The combination of the conductor tracks 8 and the U-shaped conductor bracket 6 behaves like a core wound around the ring 1 continuously at a distance wire.

With reference to FIG. 4, Fig. 5 and Fig. 6, Mon will hereinafter days the current measuring device shown in Fig. 3 according to the invention is explained. As shown in FIG. 4, the Hall element 3, which is designed as a flat plate, is first soldered upright to the corresponding connection points in the printed circuit board 7 . Subsequently, as shown in FIG. 5, the toroidal core 1 is glued to the printed circuit board 7 and to the Hall element 3 , the toroidal core 1 being arranged in such a way that the Hall element 3 formed flat is located in its air gap 2 .

Finally, the ring core 1 encompassing U-shaped conductor bracket 6 is soldered with its ends into the printed circuit board 7 , one end of a U-shaped conductor bracket 6 at the end of a conductor track 8 and the other end of this conductor bracket 6 at the end of one other conductor track 8 is soldered to, so that there is a total of all U-shaped conductor bracket 6 and all conductor tracks 8 a winding led around the ring core, which has two connection points for power supply at both ends. This final state and thus the complete construction of a Strommeßein device according to the invention is shown in Fig. 6.

Due to the construction of the current measuring device according to the invention, the manufacture is therefore considerably simplified. In particular, the disadvantageous winding of the ring core 1 forming the base body with wire is avoided. The described structure of the current measuring device according to the inven tion is considerably simpler and more compact than the previously known and implemented solutions.

The above-described current measuring device according to the inven tion and the Hall element have, however, a not insignificant temperature dependency based on the measuring principle. The solution proposed and explained below allows the current to be measured largely independently of the temperature. To better understand the principle, the equivalent circuit diagram of the Hall element shown in FIG. 7 is first explained.

At the supply input at which the supply voltage U _V is present, one can essentially see a temperature-dependent resistor R10 (T), for which the following applies:

R10 (T) = R10. (1 + TC _R10 .dT),

where dT the temperature change and R10 the input resistance stood at 20 ° C.

The output voltage U _OUT results on the one hand from the ohmic offset voltage Rofs and the actual Hall voltage U _HALL . The output resistance R20 (T) is also temperature-dependent. If you tap the Hall voltage with high impedance, e.g. B. via an impedance converter, the output resistance R20 (T) need not be taken into account.

The output voltage of the Hall element, as has already been explained previously, results in:

U _HALL (T) = U _HALL0 (T) + K (T) .k _geom .I _mess .I _V ,

where:

U _HALL0 (T) = U _HALL0 . (1 + TC _VR10 .dT),

K (T) = K0. (1 + TC _V20 ),

where U _{HALL0 is} the offset voltage at 20 ° C, K0 the gain at 20 ° C, TC _VR10 the temperature coefficient of the offset voltage and TC _V20 the temperature coefficient of the gain. The temperature coefficients of the Hall element can be found in the data sheets or easily determined by measurement.

If the Hall element is supplied with a constant supply current I _V , the result for the supply voltage U _{V is} :

U _V = I _V .R10. (1 + TC _R10 .dT).

If the supply voltage U _{V is} measured, the temperature change dT can be determined using the above equation with known supply current I _V , input resistance R10 and temperature coefficient TC _R10 :

The supply voltage U _V thus represents a measure of the temperature T of the Hall element.

The offset voltage of the Hall element can be calculated using the temperature. This is first subtracted from the measured Hall voltage U _HALL (T):

U _HALL (T) off_korr = K (T) .k _geom .I _mess .I _V ,

where U _HALL (T) off_korr is the offset-corrected Hall voltage.

There are two ways to correct the gain of the Hall element:

• 1. The supply current I _V is varied, or
• 2. the offset-corrected Hall voltage U _HALL (T) off_korr is divided by (1 + TC _V20 ) and the result is:
  U _HALL = K0.k _geom .I _mess .I _V = const..I _mess .

The Hall voltage U _HALL is therefore directly proportional to the measuring current I _mess regardless of the temperature.

The temperature compensation can be used directly as an analog one Realize circuit. But it can also be used in a digital Processing unit can be calculated.  

LIST OF REFERENCE NUMBERS

1

toroidal

2

air gap

3

Hall element

4

ladder

5

turns

6

U-shaped conductor bracket

7

Printed circuit board

8th

conductor tracks
I _mess

Current to be measured
R10 (T) Temperature dependent resistance
R20 (T) output resistance
Rof's ohmic offset voltage
U _HALL

(T) Hall element output voltage
U _OUT

output voltage
U _V

supply voltage

Claims (7)

1.Device for the galvanically isolated measurement of an electric current flowing in a conductor using a ring core with an air gap wound in several turns by the conductor and applied to a printed circuit board, in which a linear circuit board attached to the printed circuit board and also electrically connected there senes Hall element is introduced, the output voltage is proportional to the magnetic flux density of the magnetic field generated by the current to be measured and bundled in the toroid, characterized in that the turns of the conductor from U-shaped, the toroid ( 1 ) each encompassing Leiterbü gels ( 6 ) and on the printed circuit board ( 7 ) suitably arranged conductor tracks ( 8 ) are assembled, the open ends of the U-shaped conductor brackets being mechanically and electrically connected to the ends of the respectively assigned conductor tracks in such a way that an electrical contact is made via the conductor tracks Conclusion of the U-shaped conductor bracket and thus a behavior of the combination formed from the conductor tracks and the U-shaped conductor bracket results in accordance with a wire wound around the ring core. 2. Device according to claim 1, characterized in that the Hall element ( 3 ) designed as a flat plate is soldered vertically standing upright in the printed circuit board ( 7 ) to the connection points arranged there that the toroidal core ( 1 ) on the printed circuit board and is glued to the Hall element and that the ring core umgrei fenden U-shaped conductor bracket ( 6 ) with its ends in the ge printed circuit board and in each case at two connection points at the ends of two assigned conductor tracks ( 8 ) are soldered. 3. Device according to claim 2, characterized by a Assembly sequence, which is the order of the in claim 2 specified characteristics. 4. Device according to one of the preceding claims, characterized by measures for temperature compensation of the type that the output voltage (U _OUT ) is independent of the temperature directly proportional to the current to be measured (I _mess ). 5. Device according to claim 4, characterized in that for temperature compensation of the temperature-dependent output voltage
U _HALL (T) = U _HALL0 (T) + K (T) .k _geom .I _mess .I _V
of the Hall element, where
U _HALL0 (T) = U _HALL0 . (1 + TC _VR10 .dT) the temperature-dependent ohmic offset voltage of the _Hall element with the offset voltage U _{HALL0 of} the _Hall element at 20 ° C and the temperature coefficient that can be determined from data sheets or by measurement TC _{VR10 is} the offset voltage
K (T) = K0. (1 + TC _V20 ) is the temperature-dependent gain of the Hall element with the gain K0 at 20 ° C and the temperature coefficient TC _{V20 of} the gain, which can be determined from data sheets or by measurement,
k _{geom is} a constant resulting from the structure (air gap _length , etc.) and I _{meas is} the current to be measured and I _{V is} the supply current of the Hall element, with a constant supply current I _V the supply voltage U _V applied to the Hall element as a measure of the temperature of the Hall element is measured and the offset voltage of the Hall element is calculated therefrom and this is first subtracted from the measured output voltage U _HALL (T) of the _Hall element, so that there is an offset-corrected output voltage
U _HALL (T) off_korr = K (T) .k _geom .I _mess .I _{V of} the Hall element, and that the correction of the gain either by variation of the supply current I _V or by dividing the offset-corrected output voltage U _HALL (T) off_korr des Hallele ment by (1 + TC _V20 ), so that as a result a temperature-compensated output voltage
U _HALL = K0.k _geom .I _mess .I _V = const..I _{mess of} the Hall element. 6. Device according to claim 5, characterized by a Realization of temperature compensation in the form of a printed circuit board arranged analog circuit. 7. Device according to claim 5, characterized by a Realization of the temperature compensation in the form of a digita len, the processing unit that performs the calculations is arranged on the printed circuit board.