To display degrees F, the Up/Down counter is preset to 32 degrees during the
integrate input state. For temperatures 32 degrees F and above (i.e. positive input
signals), the counter counts up from 32, at the fixed clock rate during the
integrate reference state until zero-crossing. The updated display corresponds to
the temperature of the sensor in degrees F, since a 32, offset has been added and
the input signal has been multiplied by 1.8 during the integrate input state (degree
F = 1.8 degree C +32). For temperature less than 32,F (i.e. negative input
signals), the counter counts down from 32 degrees at the fixed clock rate during
the integrate reference state until either zero-crossing or the counter contents are
zero. Whichever occurs first. If zero-crossing occurs during this time (i.e. if the
temperature of the sensor is between 32,F and 0,F), the display is updated with
the polarity inverted, since the input signal was negative but the actual
temperature of the sensor in degrees F is positive. If the contents of the counter
become zero (i.e. if the temperature of the sensor in degrees F is negative), the
counter then counts up from zero until zero-crossing. The updated display
corresponds to the temperature of the sensor, (e.g. -4000 counts equals -40.00
degrees F for 0.01 degree resolution.
(8) Battery and battery charger
The battery charger circuit charges the battery whenever the unit is connected to
AC line power (see 5e (3) (c). The power switch connects a nominal 7 volts to the
power supply when the unit is turned on.
(9) Power supply
The LED display is powered directly from the nominal 7 volt input. The analog
signal conditioner and the A-D converter are powered from an inverter circuit. It
supplies 3 regulated outputs:
(a) Positive 15 volts
(b) Negative 15 volts
(c) Positive 5 volts
7. CALIBRATION PROCEDURE FOR SELF-INDICATING THERMOMETERS
(CELSIUS AND FAHRENHEIT)
a. Test Instrument Identification
This procedure provides instructions for the calibration of Self-Indicating Thermometers
(Celsius and Fahrenheit). Federal specification GG-T-336, MIL-T-1344A and NBS
Monograph 90 were used as the prime data source in compiling these instructions. The
thermometers will be referred to as the "TI" (test instrument) throughout this procedure.
(1) Model Variations. Thermometer types vary in range, accuracy and immersion
depth. This is a general procedure covering Celsius and Fahrenheit thermometers.
(2) Time and Technique. The time required for this calibration is approximately 2
hours, using the physical technique.
b. Calibration Description
TI parameters and performance specifications which pertain to this calibration are listed
in table 1.