5.3 Back View
See Figure5 on page 25.
Stand - The standat the back of the 1522 can be flipped down to prop up the
instrument for better viewing.
Battery Compartment - Behind the stand is the compartment that contains the
battery pack. The battery pack can beaccessed if necessary by opening the bat-
tery coverwith a small Philips screwdriver (see Section 6.1).
Serial Number Label - Also behind the stand is theserial number label that
uniquely identifies the instrument.
5.4 Internal Features
The significantcomponents inside the 1522 are described here.
Battery - The 1522 hasan internal rechargeable battery pack that can be re-
chargedby the AC adapter without removing the battery. It can be used and re-
chargedmany times. If necessary, it can be easily removed and replaced (see
Section 6.1).
Micro-controller- The 1522 uses a micro-controller to control all its func-
tions.The micro-controller manages the measurement process, retrieves mea-
surement data from the analog-to-digital converter(ADC), places
measurements and other information on the display,senses button actions,
reads battery status information from the powercontrol circuit, and handles
communicationsthrough the serial port.
PowerControl Circuit - The power control circuit manages the electrical
powerth at drivesall the circuits. It hand les switching between the two sources
of power(DC input and battery pack), regulates voltages, monitors the state of
batterycharge, and manages battery charging.
Analog-to-DigitalConverter and Measurement Circuit - The ADC takes an
analog signalproduced by the probe and converts it to a digital value that can
be read by themicro-controller. The ADC used in the 1522 was selected for its
excellentreso lution, linearity,and stability. The measurement circuit built
around the ADCwas carefully designed for accuracy and stability to match the
ADC. The measurement circuit allows complete rejection of probe wire resis-
tance effectsthat would otherwise seriously limit accuracy. Offsets from
sources such as thermoelectricEMF are also completely rejected. This is done
using a current reversaltechnique with the probe current alternating at a rate of
one cycleper second. Self-heating is minimized by using low sensing currents.
ForPRTs the current is only 0.5 mA. For thermistors the current is only 0.005
mA.
1522 Handheld Thermometer Readout
User’s Guide
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