Resistivity value measuring circuit

• US 4,910,689 A
• Filed: 12/17/1987
• Issued: 03/20/1990
• Est. Priority Date: 12/25/1986
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Shibamiya, Yoshikazu
• Primary Examiner(s): Lall, Parshotam S.
• Application Number:
  US07/134,035
• Time in Patent Office: 824 Days
• Field of Search: 364/556, 364/557, 364/558
• US Class Current: 702/65
• CPC Class Codes: G01K 7/24 in a specially-adapted circuit, e.g. bridge circuit
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00

Abstract

A resistivity value measuring circuit comprises: a capacitor to accumulate charges; a switch to electrically connect a device to be measured such as a thermistor with the capacitor; a transistor to discharge the charges accumulated in the capacitor; and a measuring circuit to repetitively measuring the first time and the second time by performing the connecting operation by the switch. The first time corresponds to the period of time until the voltage of the capacitor which is accumulated by only a reference device as a constant resistivity becomes a predetermined value. The second time corresponds to the period of time until the voltage of the capacitor which is accumulated by the parallel connection of the reference device and the thermistor becomes the predetermined value. A measurement value of the thermistor and the ratio of the first and second times are made correspond on the basis of the result of the measurement of the measuring circuit. With this circuit, a resistivity value of the thermistor can be cheaply and accurately detected.

Claims

1. A resitivity value measuring circuit comprising:

accumulating means for accumulating charges;

switching means for electrically connecting a target element whose resistivity value is to be measured to said accumulating means;

discharging means for discharging the charges accumulated in said accumulating means; and

measuring means for repetitively measuring a first time period and a second time period by executing the connecting operation by said switching means, wherein during the first time period, charges are accumulated in said accumulating means only through a reference element such that a voltage across said accumulating means reaches a predetermined value, and wherein during the second time period, charges are accumulated in said accumulating means through the reference element and the target element such that a voltage across said accumulating means reaches the predetermined value,

wherein the resistivity value of the target element is determined on the basis of the ratio of the first time period to the second time period.

2. A circuit according to claim 1, wherein said reference element is a reference resistor, the target element is a temperature dependency resistor, said accumulating means is a capacitor, and said switching means and said discharging means are transistors.

3. A circuit according to claim 1, further comprising means for detecting whether printing is being executed, wherein the resistivity value measurement is performed when said detecting means detects no printing.

4. A circuit according to claim 1, further comprising means for detecting whether said circuit is in a printing mode, wherein the resistivity value measurement is performed in the printing mode.

5. A method of measuring a resistivity value including:

a reference element of a known resistivity value;

a target element whose resistivity value is to be measured;

accumulating means for accumulating charges;

discharging means for discharging the charges accumulated in said accumulating means; and

measuring means for measuring a first time period and a second time period, wherein during the first time period, charges are accumulated in said accumulating means only through said reference element such that a voltage across said accumulating means reaches a predetermined value, and wherein during the second time period, charges are accumulated in said accumulating means through the reference element and the target element such that a voltage across said accumulating means reaches the predetermined value,

wherein the resistivity value of the target element is determined on the basis of the ratio of the first time period to the second time period.

6. A method according to claim 5, further comprising means for detecting whether printing is being executed, wherein the resistivity value measurement is performed when said detecting means detects no printing.

7. A method according to claim 5 wherein said reference element is a reference resistor, the target element is a temperature dependency resistor, and said accumulating means is a capacitor.

8. A method according to claim 5,further comprising means for detecting whether said circuit is in a printing mode, wherein the resistivity value measurement is performed in the printing mode.

9. A resistivity value measuring circuit comprising:

first charging means comprising a reference element;

second charging means comprising a target element whose resistivity value is to be measured;

charge accumulating means of accumulating charges through said first and second charging means;

switching means for electrically disconnecting said second chargng means from said charge accumulating means;

discharging means for discharging the charges accumulated by said charge accumulating means; and

voltage detecting means whose logic level is inverted when a voltage across said charge accumulating means reaches a predetermined value,

wherein a first time period is measured starting when said second charging means is disconnected from said charge accumulating means by said switching means after discharge by said discharging means and ending when the logic level of said voltage detecting means is inverted, the charges being accumulated by said charge accumulating means only through said first charging means during the first time period,

wherein a second time period is measured starting when said switching means is turned off after discharge by said discharging means and ending when the logic level of said voltage detecting means is inverted, the charges being accumulated by said charge accumulating means through said first and second charging means during the second time period,

wherein the resistivity value of the target element is determined on the basis of the ratio of the first time period to the second time period.

10. A circuit according to claim 9, wherein said reference element is a reference resistor, said target element is a temperature dependency resistor, said charge accumulating means is a capacitor, said voltage detecting means consists of a comparator and a reference voltage to consists of a logic IC, and said switching means and said discharging means are transistors.

11. A circuit according to claim 9, further comprising means for detecting whether printing is being executed, wherein the resistivity value measurement is performed when said detecting means detects no printing.

12. A circuit according to claim 9, further comprising means for detecting whether said circuit is in a printing mode, wherein the resisitvity value measurement is performed in the printing mode.