Electronic Thermometer

• US 4,838,707 A
• Filed: 07/17/1987
• Issued: 06/13/1989
• Est. Priority Date: 02/01/1984
• Status: Expired due to Term

• Current Assignee: Seiko Epson Kabushiki Kaisha (Seiko Group)
• Original Assignee: Kabushiki Kaisha Suwa Seikosha, Shiojiro Kogyo Kabushiki Kaisha
• Inventors: Hosaka, Toshiyuki, Ozawa, Masaki, Yoshizawa, Masayuki
• Primary Examiner(s): Shoap, Allan N.
• Assistant Examiner(s): Worth, W. Morris
• Application Number:
  US07/077,086
• Time in Patent Office: 697 Days
• Field of Search: 374/170-173, 374/179, 374/181, 374/183, 374/185, 377/25, 128/736
• US Class Current: 374/171
• CPC Class Codes: G01K 1/028 arrangements for numerical indication
• CPC Class Codes: H03M 1/1023 Offset correction H03M1/1019 takes precedence; removal of offset already present on the analogue input signal H03M1/1295
• CPC Class Codes: H03M 1/52 Input signal integrated with linear return to datum
• CPC Class Codes: H03M 1/60 with intermediate conversion to frequency of pulses

Abstract

An electronic thermometer is provided in which the number of pulses counted in a first count and the number of pulses counted in a second count are respectively proportional to the resistance of a reference resistance and that of a thermosensing element. When the first counted value is to be adjusted so as to realize the absolute value adjustment of the thermometer, the difference between the resistance of the thermosensing element and the resistance of the reference resistor is adjusted by varying the number of counts in a counter upon whose content the timing of the second count depends. Accordingly, the absolute value precision adjustment of the electronic thermometer is realized by providing an initial logic adjustment circuit in which the number of the first clock counts is appropriately varied.

Claims

1. An electronic measuring device comprising:

sensing means having a physical property which varies in response to a quantity to be measured;

reference means having a physical property like that of the sensing means but which is substantially invariant in response to variations of the quantity being measured;

permanently programmable storage means for providing a predetermined initial logic adjustment value which represents the difference between the absolute values of the sensing means and the reference means;

converter means for measuring the reference means during a first measurement period to provide a reference count value and for measuring the sensing means during a second measuring period to provide a sensing count value, each count value being proportional to the respective measurements;

comparing means having the initial logic adjustment value, the reference count value, and the sensing count value as inputs, the comparing means providing a signal when the sum of the reference count and the initial logic adjustment value attains a predetermined value and a corrected sensing count value as an output at the end of the second measuring period;

controller means responsive to the signal from the comparing means for establishing the length of the second measuring period; and

means for changing the corrected sensing count value into a digital value for display of the measured quantity.

2. An electronic device in accordance with claim 1, wherein the comparing means further comprises coincidence detecting means having the adjusted reference count value as an input and the coincidence detecting means initiating measurement of the sensing means when the adjusted reference count reaches a predetermined level.

3. An electronic measuring device in accordance with claim 2 in which the measured quantity is temperature, the reference means comprises a reference resistor, and the sensing means comprises a thermosensing element.

4. An electronic measuring device in accordance with claim 2 in which the comparing means comprises a resettable-1/2 divider into which the initial logic adjustment value is set.

5. An electronic measuring device in accordance with claim 2 in which the comparing means comprises a counter having a low bit portion which comprises a set-priority resettable-1/2 divider and having a high bit portion which comprises a resettable-1/2 divider, and a multiple input gate having the data in the dividers and the initial logic adjustment value as inputs.

6. An electronic measuring device in accordance with claim 3 in which the converting means comprises a resistance-to-frequency converter and the comparing means comprises a counter having the output of the resistance-to-frequency converter as an input.

7. An electronic measuring device in accordance with claim 6 in which the comparing means further includes a divider having the first count value and the initial logic adjustment value as inputs, there being a multiple-input NAND gate connected across the divider to detect coincidence and to provide the signal for establishing the length of the second measurement period.

8. An electronic measuring device in accordance with claim 7 in which the resistance-to-frequency converter further comprises a capacitor, the measuring device further comprising:

switching means responsive to at least one control signal for connecting one of the reference resistor and the sensing means to the capacitor for measurement.

9. An electronic measuring device in accordance with claim 7 in which the resistance-to-frequency converter further comprises:

logic means for cyclically charging and discharging the capacitor for a first period through the reference resistor and for a second, equal period, through the sensing means to provide the reference count value and the sensing count value.

10. An electronic measuring device in accordance with claim 8 in which the switching means comprises a switch responsive to a first control signal for connecting the reference resistor to the capacitor and a second switch responsive to a second control signal for connecting the sensing means to the capacitor, the controller means providing the first control signal to the first switch and, when the signal from the comparison means has been received, providing the second control signal to the second switch.

11. The electronic measurement device of claim 3 in which the converting means comprises a double-integration converter and the comparing means comprises a counter, and further comprising:

clock means having a train of clock pulses as an output, the clock signals being input to the counter; and

controller means having the clock pulses and the output of the double-integration converter as inputs, the controller means feeding a control signal to the counter when integrating measurement of the reference means is complete, whereby counting of the sensing value is initiated.

12. The electronic measuring device of claim 11 in which the comparing means comprises a multiple-input AND gate having the reference count value as an input and feeding the signal to the controller means to terminate measurement of the reference means.

13. The electronic measuring device of claim 11 in which the controller means outputs at least one switching signal and further comprising:

a capacitor as the integrating element in the double-integrating converter;

switch means responsive to the switching signal for connecting one of the reference means and a predetermine voltage, and the sensing means and the predetermined voltage, to the capacitor as first and second intergrating elements, whereby an operational amplifier means provides one of an integrated reference signal and an integrated sensing signal to the controller means.

14. An electronic measuring device in accordance with claim 3 in which the means for changing the corrected sensing count value into a digital value for display comprises:

latch means for storing the corrected sensing count value;

read-only-memory means for converting the corrected sensing count value into a temperature value;

means for decoding the output of the read-only-memory;

driver means receiving the decoded signal; and

display means responsive to the driver means for displaying the measured temperature.

15. An electronic measuring device in accordance with claim 3 wherein the means for changing the corrected sensing count value into a digital value for display comprises:

latch means for storing the corrected sensing count value;

read-only-memory means for converting the stored corrected sensing count value into a value representative of the quantity measured;

driver means having the converted value of the read-only-memory means as an input; and

display means responsive to the output of the driver means to display the measured temperature.

16. An electronic measuring device in accordance with claim 3 wherein the means for changing the corrected sensing count value into a digital value for display further comprises:

latch means having the corrected sensing count value as an input;

decoder means having the value latched in the latch means as an input;

driver means having the decoded signal from the decoder means as an input; and

display means responsive to the output of the driver circuit to display the measured temperature.

17. An electronic measuring device in accordance with claim 3 and further comprising:

means responsive to a control signal for making a measured value available for independent measurement.

18. An electronic measuring device in accordance with claim 3 in which the converter means comprises a resistance-to-frequency converter.

19. An electronic measuring device in accordance with claim 3 in which the converter means comprises a double-integration converter.

20. An electronic measuring device comprising:

thermosensing means having a resistance which varies in response to a temperature to be measured;

reference resistor means having a resistance which is substantially invariant;

resistance-to-frequency converter means for measuring the reference resistor means during a predetermined period and the thermosensing means during a sensing period to respectively provide a reference count value and a sensing count value, each count value being proportional to the respective measurements;

divider means having the reference count value and the sensing count value as inputs and having a corrected sensing count value as an output;

means coupled to the divider means for correcting the reference count value by the addition thereto of a predetermined initial logic adjustment value which represents the difference between the absolute values of the thermosensing means and the reference means so as to provide a corrected reference count value;

multiple-input NAND gate means responsive to the corrected reference count value to establish the length of the sensing period; and

means for changing the output of the divider means into a digital value for display of the measured quantity.

21. An electronic measuring device in accordance with claim 20 in which the resistance-to-frequency converter further comprises a capacitor, the measuring device further comprising:

switching means responsive to at least one control signal for connecting one of the reference resistor means and the thermosensing means to the capacitor for measurement.

22. An electronic measuring device in accordance with claim 21 in which the resistance-to-frequency converter further comprises:

logic means for cyclically charging and discharging the capacitor through a reference resistor means during the predetermined period and through the thermosensing means during the sensing period to respectively provide the reference count value and the sensing count value.

23. An electronic measuring device in accordance with claim 22 in which the NAND gate means provides a sensing period control signal and in which the switching means comprises a switch responsive to a first control signal for connecting the reference resistor to the capacitor and a second switch responsive to a second control signal for connecting the thermosensing means to the capacitor and further comprising:

controller means having the sensing period control signal as an input, the controller means providing the first control signal to the first switch and, when the sensing period control signal is received, providing the second control signal to the second switch.