1. A method for determining whether a probe has been placed over substantially homogenous tissue, wherein the probe measures the impedance of human or animal body tissue, the probe comprising at least a first, a second, a third and a fourth electrode arranged such that the third and fourth electrodes are each located substantially the same distance from both the first and second electrodes; the method comprising:
driving a current between the first and the second electrode while simultaneously measuring a first value of an electrical parameter between the third and fourth electrode; and
determining whether the probe has been placed over substantially homogenous tissue based on the first value or a calculation based on the first value, wherein if the first value or a calculation based on the first value is substantially equal to zero then it is determined that the probe has been placed over substantially homogenous tissue.
2. The method according to claim 1 for use with a probe wherein the first, second, third and fourth electrodes are arranged at the corners of a square with the first and second electrodes diagonally opposite each other.
3. A computer program product comprising a non-transitory computer readable medium bearing a computer program comprising code means that, when executed on a computer system, instructs the computer system to perform the method according to claim 1.
4. A computer program product comprising a non-transitory computer readable medium bearing a computer program comprising code means that, when executed on a computer system, instructs the computer system to perform the method according to claim 2.
5. A probe configured to measure the impedance of human or animal body tissue, the probe comprising:
at least a first, a second, a third, and a fourth electrode arranged such that the third and the fourth electrodes are each located substantially the same distance from both the first and second electrodes;
a current source for driving a current between the first and second electrodes;
a measurement circuit for measuring a first value of an electrical parameter between the third and fourth electrodes simultaneously as the current source drives the current;
a controller for controlling the current source; and
a processor for determining whether the probe has been placed over substantially homogenous tissue based on the first value or a calculation based on the first value, wherein the processor determines that the probe has been placed over substantially homogenous tissue if the first value or a calculation based on the first value is substantially equal to zero.
6. The probe according to claim 5, wherein the first, second, third and fourth electrodes are arranged at the corners of a square with the first and second electrodes diagonally opposite each other.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. Method for capacitive seat-occupancy recognition that is based on:
CREF whereby CREF is the known capacitance of a reference capacitor with capacitance CREF with respect to a first reference potential of a vehicle,
CX whereby CX is the capacitance of a seat sensor electrode integrated into a seat with respect to the first reference potential,
CY whereby CY is the at least a parasitically-present capacitance of the sensor electrode with respect to a second reference potential or of the vehicle ground,
and on a first switch (S1) that connects the reference capacitor and a reference-voltage source of known voltage UREF with the first reference potential,
and on a second switch (S2) that connects the sensor electrode with the reference capacitor,
and on a third switch (S3) that connects the sensor electrode with the reference potential,
said method comprising the following steps to recognize the seat-occupancy status of the seat:
a1 charging the reference capacitor to the voltage UREF of the reference-voltage source by opening the second switch (S2) and closing the first switch (S1), and discharging of capacitors CX and CY by closing the third switch (S3),
b1 opening the first switch (S1) and of the third switch (S3) to create a state of oscillations in which the capacitance CREF and the capacitors CX and CY retain their charge,
c1 closing the second switch (S2) so that the charge of the capacitance Cur is distributed to the capacitors CREF, CX and CY and a first resulting voltage URES arises that is stored whereby
U
RES
=
U
REF
\xb7
C
REF
C
REF
+
C
X
+
C
Y
applies,
d1 comparing the resulting voltage URES with stored limit values assigned to specific occupancy-seat statuses, and
e1 deriving of an occupancy seat status from the comparison.
2. Method for capacitive seat-occupancy recognition per claim 1, wherein it is additionally based on
a fourth switch (S4) that connects the connection point of the reference capacitor to the first switch (S1) and the second switch (S2) to the first reference potential, and
a fifth switch (S5) that connects the connection point of the sensor electrode to the second switch (S2), and the third switch (S3) to the reference-voltage source with voltage UREF,
wherein
a step a2.0 is performed before step a1 in which the fourth switch (S4) and the fifth switch (S5) are opened,
a step c2.1 is performed after step c1 in which the second switch (S2) is again opened and subsequently the reference capacitor is discharged to the first reference potential by closing of the fourth switch (S4), and the fifth switch (S5) is closed in order to charge the capacitors CX and CY up to the reference voltage UREF of the reference-voltage source,
a step c2.2 is subsequently performed in which the fourth switch (S4) and the fifth switch (S5) are opened so that an oscillation condition exists in which the capacitance CREF and the capacitors CX and CY retain their charge,
a step c2.3 is subsequently performed in which the second switch (S2) is closed so that the charge of the capacitors CX and CY is distributed to the capacitors CREF, CX and CY and a second resulting voltage U\u2032RES is set wherein
U
RES
\u2032
=
U
REF
\xb7
C
X
+
C
Y
C
REF
+
C
X
+
C
Y
applies,
then step d2 is performed after step d1 in which additionally the second resulting voltage U\u2032RES andor the differential between both resulting voltages URES and U\u2032RES with stored limit values assigned to specific occupancy or seat statuses are compared, and
a step f2 is performed after step e1 in which the differential between the reference voltage URES and the sum of the resulting voltages URES and U\u2032RES is compared with the stored values in order to recognize any charge loss arising during the performed test, and thus to validate or alter the result of the derivation of the occupancy status from the comparison in Step e1.
3. Method for capacitive seat-occupancy recognition per claim 1, wherein additionally the following is taken into account:
a thermal conductor that is a component of a seat heater of the seat, wherein the one end of the thermal conductor is connected via a sixth switch (S6) to an operating-voltage source with voltage UB, that for its part is connected to the vehicle ground, and the other end is connected via a seventh switch (S7) with the vehicle ground (3), by means of which the at least parasitically-present capacitance CY between the connection point of the sensor electrode is connected to the second switch (S2) and to the third switch (S3) on the one side and on the other side with the thermal conductor, and
the method is based on an at least parasitic external capacitance CEXT, that on the one side is connected to the first reference potential or to the vehicle ground and on the other side is connected with the thermal conductor, and whereby furthermore this connection point is connected via an eighth switch (S8) to a second reference-voltage source with voltage U*REF, preferably defined as
U
REF
*
\u2245
U
REF
\xb7
C
REF
C
REF
+
C
X
with capacitance CX for the case of the unoccupied seat,
that for its part is connected to a first reference potential or the vehicle ground, and furthermore this connection point is connected via a ninth switch (S9) with the reference potential of the reference-voltage source U*REF,
wherein
a step a3.0 is performed before step a1 in which the sixth switch (S6) and the seventh switch (S7) are opened in order to render the thermal conductor voltage-free,
a step a3.1 is performed after step a1 in which the at least parasitic capacitance CEXT is discharged by closing of the ninth switch (S9),
a step c3.1 is performed after step c1 in which the reference capacitor CREF is charged to the voltage Umm of the first reference-voltage source by opening the second switch (S2) and by closing the first switch (S1), and the capacitors CX and CY are discharged by closing the third switch (S3), and it is additionally ensured that the additionally at least parasitically-present capacitance CEXT remains discharged in that the ninth switch (S9) remains closed,
a step c3.2 is then performed in which a state of oscillation is created by opening the first switch (S1) and the third switch (S3) and by opening the ninth switch (S9), in which the parasitically present external capacitance CEXT the capacitors CREF, CX, CY retain their charge,
a step c3.3 is then performed in which the charge of the reference capacitors is distributed to the capacitors CREF and CX by closing the second switch (S2) and by simultaneous closing of the eighth switch (S) and the voltage U*REF is simultaneously present at the connection between the capacitors CY and CEXT and the eighth switch (S8), which achieves the fact that the voltage increase at the parasitically-present coupling capacitor CY turns out to be smaller than in step c1, whereby for the resulting voltage U*RES approximately
U
RES
*
=
U
REF
\xb7
C
REF
C
REF
+
C
X
+
A
\xb7
C
Y
,
with A<1, applies,
that is stored, whereby A is a factor that is dependent on the voltage of the second reference-voltage source U*REF and the occupancy status of the seat, whereby A upon selection of U*REF in the case of the unoccupied seat is near zero, and in the case of the occupied seat will not be greater than 1, then a decision is made from the comparison in step d1 and the derivation from step e1 regarding the seat status, and a specific occupancy status is assigned through a comparison of URES and U*RES with stored limit values for the occupancy statuses.
4. Apparatus for capacitive seat-occupancy recognition comprising:
a reference capacitor that possesses a capacitance CREF with respect to a first reference potential of a vehicle,
electrodes integrated into a seat sensor that possess a capacitance CX with respect to a first reference potential,
at least parasitically-present capacitance auf CY of the sensor electrode with respect to a second reference potential or the vehicle ground,
a first switch (S1) that connects the reference capacitor and a reference-voltage source of known voltage UREF connected with the reference potential,
a second switch (S2) that connects the sensor electrode with the reference capacitor, and
a third switch (S3) that connects the sensor electrode with the reference potential, and the at least parasitically-present capacitance with the vehicle ground.
5. Apparatus as defined in claim 4, wherein a fourth switch (S4) connects the connection point of the reference capacitor to the first switch (S1) and the second switch (S2) with the first reference potential, and wherein a fifth switch (S5) connects the connection point of the sensor electrode to the second switch (S2) and the third switch (S3), and connects the at least parasitically-present capacitance CY of the sensor electrode with the reference-voltage source.
6. Apparatus as defined in claim 4, further comprising a thermal conductor, which is a part of a seat heater of the seat, wherein one end of the thermal conductor is connected via a sixth switch (S6) with an operating-voltage source, that for its part is connected to the vehicle ground, and the other end is connected via a seventh switch (S7) with the vehicle ground, by means of which the at least parasitically-present capacitance CY between the connection point of the sensor electrode is connected with the second switch (S2) and with the third switch (S3) on the one side and on the other side with the thermal conductor, and
an at least parasitically-present external capacitance CEXT, that on the one side is connected to the first reference potential or to the vehicle ground and on the other side is connected to the thermal conductor, and whereby furthermore this connection point is connected via an eighth switch (S8) with a second reference-voltage source U*REF, with
U
REF
*
\u2245
U
REF
\xb7
C
REF
C
REF
+
C
X
for the case of an unoccupied seat being neglected by the parasitic capacitance CY, and furthermore this connection point is connected via a ninth switch (S9) with the reference potential of the second reference-voltage source.
7. Apparatus as defined in claim 6, wherein the voltage for the second reference-voltage source is extracted from the reference-voltage source with voltage UREF, and a capacitance CCTRL is formed between the thermal conductor and the connection between the eighth switch (S8) and the ninth switch (S9) to imitate the voltage U*REF of the second reference-voltage source, whereby for the value of the capacitance CCTRL
C
CTRL
\u2245
C
EXT
\ue89e
U
REF
*
U
REF
–
U
REF
*
applies.
8. Apparatus as defined in claim 7, wherein the first switch (S1) and the fourth switch (S4) are no longer connected directly with the reference capacitance Ca in that a new network node (PREF) is formed by the connection of the first switch (S1) and of the fourth switch (S4), and an additional channel-selector switch (S0) is provided that creates the connection between the newly-established network nodes (PREF) on the one side, and between the reference capacitance CREF and the second switch (S2) on the other side.
9. Apparatus as defined in claim 8, wherein the sixth switch (S6) and the seventh switch (S7) are each implemented using a MOSFET (T6, T7) with electronic triggering circuit (MOSFET triggering device) whereby the external capacitance CEXT represents at least one-half of the drainsource capacitors of each of the two MOSFETs (T6, T7) that is visible in the blocked condition of the MOSFETs.
10. Apparatus as defined in claim 9, wherein the first through fifth switches (S1 through S5), the eighth switch (S8), the ninth switch (S9), and the reference capacitance CREF are formed by a micro-controller with a sample-and-hold capacitor in an Analog-to-Digital converter (ADC) for Cm and with a channel multiplexer (MUX) before the ADC for the first switch (S1), the second switch (S2) and the fourth switch (S4) and with a first port driver (P1) for the third switch (S3) and the fifth switch (S5), and with a second port driver (P2) for the eighth switch (S8) and the ninth switch (S9).
11. Apparatus as defined in claim 9, wherein the first through fifth switches (S1 through S5), the eighth switch (S8), the ninth switch (S9) and the reference capacitance Cam are formed by a micro-controller with sample-and-hold capacitor in an analog-to-digital converter (ADC) for CREF and with a channel multiplexer (MUX) for the second switch (S2) and the additional channel-selector switch (S0), and with a first port driver (P1) for the third switch (S3) and the fifth switch (S5), and with a second port driver (P2) for the eighth switch (S8) and the ninth switch (S9), or with a second port driver (P2) for triggering of the eighth switch (S8) and triggering of the ninth switch (S9), and with a third port driver (P3) for the first switch (S1) and the fourth switch (S4).
12. Apparatus as defined in claim 4, wherein the first through fifth switches (S1 through S5), the eighth switch (S8), the ninth switch (S9), and the reference capacitance CREF are formed by a micro-controller with a sample-and-hold capacitor in an Analog-to-Digital converter (ADC) for CREF and with a channel multiplexer (MUX) before the ADC for the first switch (S1), the second switch (S2) and the fourth switch (S4) and with a first port driver (P1) for the third switch (S3) and the fifth switch (S5), and with a second port driver (P2) for the eighth switch (S8) and the ninth switch (S9).
13. Apparatus as defined in claim 5, wherein the first through fifth switches (S1 through S5), the eighth switch (S8), the ninth switch (S9), and the reference capacitance CREF are formed by a micro-controller with a sample-and-hold capacitor in an Analog-to-Digital converter (ADC) for CREF and with a channel multiplexer (MUX) before the ADC for the first switch (S1), the second switch (S2) and the fourth switch (S4) and with a first port driver (P1) for the third switch (S3) and the fifth switch (S5), and with a second port driver (P2) for the eighth switch (S8) and the ninth switch (S9).
14. Apparatus as defined in claim 5, wherein the first switch (S1) and the fourth switch (S4) are no longer connected directly with the reference capacitance CREF in that a new network node (PREF) is formed by the connection of the first switch (S1) and of the fourth switch (S4), and an additional channel-selector switch (S0) is provided that creates the connection between the newly-established network nodes (PREF) on the one side, and between the reference capacitance CREF and the second switch (S2) on the other side.
15. Apparatus as defined in claim 14, wherein the sixth switch (S6) and the seventh switch (S7) are each implemented using a MOSFET (T6, T7) with electronic triggering circuit (MOSFET triggering device) whereby the external capacitance CEXT represents at least one-half of the drainsource capacitors of each of the two MOSFETs (T6, T7) that is visible in the blocked condition of the MOSFETs.
16. Apparatus as defined in claim 15, wherein the first through fifth switches (S1 through S5), the eighth switch (S8), the ninth switch (S9) and the reference capacitance CREF are formed by a micro-controller with sample-and-hold capacitor in an analog-to-digital converter (ADC) for CREF and with a channel multiplexer (MUX) for the second switch (S2) and the additional channel-selector switch (S0), and with a first port driver (P1) for the third switch (S3) and the fifth switch (S5), and with a second port driver (P2) for the eighth switch (S) and the ninth switch (S9), or with a second port driver (P2) for triggering of the eighth switch (S8) and triggering of the ninth switch (S9), and with a third port driver (P3) for the first switch (S1) and the fourth switch (S4).