Method and apparatus for digitizing a voltage

• US 20030117098A1
• Filed: 11/18/2002
• Published: 06/26/2003
• Est. Priority Date: 12/22/2001
• Status: Active Grant

• Current Assignee: Ebm-Papst St Georgen GmbH & Company KG (Ebm-Papst Mulfingen GmbH & Company KG)
• Original Assignee: Papst-Motoren GmbH & Company KG (Ebm-Papst Mulfingen GmbH & Company KG)
• Inventors: Kuner, Arnold, Berroth, Hansjorg, Schondelmaier, Hans-Dieter
• Granted Patent: US 6,949,903 B2
• Time in Patent Office: Days
• US Class Current: 318/440
• CPC Class Codes: H03M 1/145 the steps being performed sequentially in series-connected stages H03M1/141, H03M1/143, H03M1/16 take precedence
• CPC Class Codes: H03M 1/34 Analogue value compared with reference values H03M1/48 takes precedence
• CPC Class Codes: H03M 1/54 Input signal sampled and held with linear return to datum

Abstract

A method of digitizing a voltage comprises the following steps: A capacitor (80) is charged, through an impedance, to a voltage value (Um) dependent on the voltage to be digitized; that one of a plurality of voltage ranges in which, i.e. the limits between which, said voltage value (Um) lies, is ascertained, and the two limits of that voltage range are defined as a first limit and second limit; the voltage at the capacitor (80) is modified to the first limit by means of a charge modification circuit containing an impedance (84), and a first time interval (T1) needed therefor is identified; the voltage at the capacitor (80) is modified to the second limit; the voltage at the capacitor (80) is modified from the second to the first limit via the charge modification circuit. A second time interval (T2) needed therefor is identified. Based on values of the first time interval (T1) and second time interval (T2), a digital value (LSB) is calculated, which serves as an indication of how much the voltage value (Um) at the capacitor (80) differs from one of said two limits. A device for carrying out this method, and its use in an electronically commutated motor, are also described.

Claims

1. A method of digitizing a voltage, comprising the steps of;

charging a capacitor (80), through an impedance, to a voltage value (Um) which is a function of the voltage to be digitized;

ascertaining within which one of a plurality of voltage ranges said voltage value (Um) lies, each voltage range being defined by a respective first limit and respective second limit;

modifying, by means of a charge modification circuit containing an impedance, the voltage at the capacitor (80) to the first limit, and ascertaining a first time interval (T1) needed therefor;

modifying, by means of the charge modification circuit, the voltage at the capacitor (80) from the second limit to the first limit, and ascertaining a second time interval (T2) needed therefor;

calculating, based on the first time interval (T1) and second time interval (T2), a digital value which serves as an indication of how much the voltage value (Um) at the capacitor (80) differs from one of the two limits of the ascertained voltage range.

2. The method of claim 1, wherein said step of charging said capacitor comprises

connecting an impedance converter (66) having an input (72) and an output (68) to a voltage source (62) and using an output signal of said impedance converter to charge said capacitor (80).

3. The method of claim 1, further comprising

applying a substantially constant voltage value to a resistor chain (22) in the form of a series circuit of resistors (24, 26, 28, 30), connected via connecting points (32, 34, 36, 38);

and

successively comparing the respective potentials at the connecting points (32, 34, 36, 38) to the voltage value (Um) at the capacitor (80), in order to determine the first limit and the second limit of one of said voltage ranges.

4. The method of claim 3, further comprising the step of:

testing whether the voltage value (Um) at the capacitor (80) is greater than the potentials at all the connecting points of the resistor chain and, if so, connecting a resistor (94) in parallel with the capacitor (80), in order to reduce the voltage value at said capacitor (80); and

thereafter again comparing the potentials at the connecting points to the voltage value (Um) at the capacitor (80), in order to determine the first limit and the second limit.

5. The method of claim 1, further comprising

executing a routine whose program steps (FIG. 6:

S232, 234, 236) serve to control an electric motor (156) between said step of ascertaining the first time interval (T1) and said step of ascertaining the second time interval (T2).

6. The method of claim 1, further comprising

executing, between the measurement of the second time interval (T2) and the evaluation of the second time interval, a routine whose program steps (S232, S234, S236) serve to control an electric motor (156).

17. Use of a method according to claim 1 for temperature-dependent control of the rotation speed of a fan (156, 83).

18. Use according to claim 17, for digitization of a temperature for temperature-dependent control of the rotation speed of a fan (156, 83).

19. Use according to claim 17,

wherein execution of the method is controlled by the instantaneous position of the rotor (162) of a motor (156) that drives the fan (83).

7. An arrangement for digitizing a voltage, said arrangement comprising:

a capacitor (80);

a charging circuit (66, 76) having an input (62) connected to a voltage to be digitized, said charging circuit comprising an impedance (76) and serving to charge said capacitor (80) to a voltage value (Um) which is a function of the voltage to be digitized;

a microprocessor (20) for coarse classification of said voltage value (Um) into one of a plurality of voltage ranges, which voltage ranges are each defined by a respective first limit and a respective second limit;

a charge modification apparatus (84, 88) for modifying the voltage at the capacitor (80) to the first limit of the voltage range identified by said coarse classification and for measuring a first time interval (T1) needed for such modification;

a charge modification apparatus (84, 90) for modifying the voltage at the capacitor (80) to the second limit of the voltage range identified;

a charge modification apparatus (84, 88) for modifying the voltage at the capacitor (80) from the second limit to the first limit and for measuring a second time interval (T2) needed therefor; and

a calculation apparatus (44) for calculating a second digital value (LSB), based upon values of the first time interval (T1) and the second time interval (T2).

8. The arrangement according to claim 7,

wherein the microprocessor (20) serves to control (FIGS. 1:

A, B) at least one charge modification apparatus (88, 90).

9. The arrangement according to claim 7, w

herein a measurement range switchover apparatus (94, 96), controlled by the microprocessor (20), is provided, and is activated if the voltage value (Um) at the capacitor (80) is outside the available voltage ranges.

10. The arrangement according to claim 7,

wherein a calculation apparatus (FIG. 3:

S144) is provided which calculates, from a digital value (MSB) obtained by coarse classification and from the second digital value (LSB), a combined digital value that has a greater accuracy than the value obtained by coarse classification.

11. The arrangement according to claim 7,

wherein there is provided, in the charging circuit (66, 76) of the capacitor (80), an impedance converter (66) which is controllable on an input side thereof by a voltage source (52, 60, 64) whose analog voltage is to be transformed into a digital signal.

12. The arrangement according to claim 7,

wherein the microprocessor (20) also serves to control commutation of an electronically commutated motor (156).

13. The arrangement according to claim 12, further comprising a program (FIG. 3) executed by the microprocessor (20), which program includes various program calls for the digitization process, only part of the digitization process being executed at each call.

14. Use of an arrangement according to claim 7, for temperature-dependent control of the rotation speed of a fan (156, 83).

15. Use according to claim 14, for digitization of a temperature for temperature-dependent control of the rotation speed of a fan (156, 83).

16. Use-according to claim 14,

wherein the arrangement for rotation speed control is controlled by the instantaneous position of the rotor (162) of a motor (156) driving the fan (83).