Measuring device for capacitive pressure measure
A measuring device is disclosed for capacitive pressure and/or temperature measurement, particularly for tire pressure control systems, having at least one sensor, which has a capacitive measuring element to detect a state value, which is applied at an output-side measuring node of the measuring element, with at least one A/D converter operating according to the dual-slope method, with a charging/discharging circuit, for mutual charging and discharging of the measuring element and for generating a sawtooth-shaped measuring potential at the measuring node as a measure for the capacitance of the measuring element, with a period counter, which determines the periods of the measuring potential, and with a clock counter, which determines the cycles of a clock signal, which lie within the duration of at least one period of the measuring potential. The invention relates to a measuring method for capacitive pressure and/or temperature measurement.
1. A measuring device for capacitive pressure and/or temperature measurement for tire pressure control systems, the measuring device comprising:
at least one sensor, which has a measuring element for detecting a state value that is applied at an output-side measuring node of the measuring element;
at least one A/D converter operating according to a dual-slope method;
a charging/discharging circuit for charging and discharging the measuring element and for generating a sawtooth-shaped measuring potential at the measuring node as a measure for a capacitance of the measuring element;
a period counter, which determines the periods of the measuring potential; and
a clock counter, which determines cycles of a clock signal that lie within a duration of at least one period of the measuring potential.
2. The measuring device according to claim 1 , further comprising an oscillator that generates an oscillator clock signal on an output side, a frequency of the oscillator clock signal being at least higher than a frequency of the measuring potential.
3. The measuring device according to claim 1 , wherein the period counter on an output side outputs a first counter reading signal as a measure for the counted periods of the measuring potential, and wherein the clock counter on the output side outputs a second counter reading signal as a measure for the counted cycles of the clock signal.
4. The measuring device according to claim 1 , wherein the period counter and/or the clock counter are an up-counter or a down-counter, which increment or decrement by plus one their counter reading with each period of the measuring potential or with each cycle of the clock signal.
5. The measuring device according to claim 1 , wherein the charging/discharging circuit has at least one switchable current source to generate the sawtooth-shaped measuring potential.
6. The measuring device according to claim 1 , wherein the charging/discharging circuit, to generate the sawtooth-shaped measuring potential has a threshold switch, which is connected downstream of the measuring node, for comparing the measuring potential with a predefined top and bottom threshold value and which changes the control signal to drive the controllable switches with the exceeding of the measuring potential above a top threshold value or falling of the measuring potential below a lower threshold value in such a way that the charging/discharging process of the element to be measured is thereby reversed.
7. The measuring device according to claim 1 , wherein the sensor has a capacitor array, which has, in addition to the measuring element, at least one capacitive reference element as a reference for the measuring element for determining the state value.
8. The measuring device according to claim 1 , wherein the state value is a tire-specific parameter, a tire pressure, or a tire temperature.
9. The measuring device according to claim 1 , wherein the sensor is a capacitive pressure sensor for detecting a pressure.
10. The measuring device according to claim 1 , wherein the measuring element is a capacitive measuring element.
11. The measuring device according to claim 1 , wherein the charging/discharging circuit has at least one first current source for charging a capacitive element to be measured in and at least one second current source for discharging the capacitive element to be measured, wherein at least one controllable switch is disposed between each current source and the measuring node for mutual charging and discharging.
12. The measuring device according to claim 11 , wherein the controllable switch is driven by a control signal that is derived from the measuring potential in such a way that either the first or the second current source is activated.
13. The measuring device according to claim 1 , wherein the capacitor array has at least two correction capacitors, which are provided for averaging out an uncorrelated noise, which arises when the measuring potential exceeds a top reference threshold or falls below a bottom reference threshold.
14. The measuring device according to claim 13 , wherein a first correction capacitor has twice a capacitance value as a second correction capacitor.
15. A measuring method for capacitive pressure measurement for tire pressure control systems, the method comprising the steps of:
providing a capacitive element having a measuring potential that varies with pressure;
subjecting the capacitive element to a pressure to be measured;
repeatedly measuring the measuring potential of the capacitive element; and
averaging an uncorrelated noise, which occurs due to an exceeding or falling of the measuring potential above an upper reference threshold or below a lower reference threshold, respectively.
16. The method according to claim 15 , wherein a measuring device repeatedly measures the measuring potential of the capacitive element, the measuring device comprising:
at least one sensor, which has a measuring element for detecting a state value that is applied at an output-side measuring node of the measuring element;
at least one A/D converter operating according to a dual-slope method;
a charging/discharging circuit for charging and discharging the measuring element and for generating a sawtooth-shaped measuring potential at the measuring node as a measure for a capacitance of the measuring element;
a period counter, which determines the periods of the measuring potential; and
a clock counter, which determines cycles of a clock signal that lie within a duration of at least one period of the measuring potential.
17. The method according to claim 15 , wherein a dual-slope measuring method is used for the capacitance measurement.
18. The method according to claim 17 , wherein a clock signal, whose frequency is at least higher than a frequency of the measuring potential, is used for measuring the measuring potential.
19. The method according to claim 18 , wherein both cycles of the clock signal and a period of the measuring potential are counted.