PART ONE - INTRODUCTION SECTION 1 - GENERAL INFORMATION
Rev. 9-898 Model 692P
-7-
PART ONE - INTRODUCTION
SECTION 1 - GENERAL INFORMATION
1.1 Instrument Capability
Input Versatility
Display Readouts
Operator Interface
Output Flexibility
Operator Safety
1.2 Battery Backup
The instrument may be used with any GLI Differential Tech-
nique pH sensor that has an integral preamplifier (identified
by its 5-wire cable) or a conventional pH combination elec-
trode with integral or separate temperature sensor. A switch
sets the Model 692 for use with a 300 ohm thermistor or
1000 ohm RTD temperature sensor input to compensate the
pH measurement for variations in temperature.
The large liquid crystal display can alternately indicate four
variables: pH, temperature (in °C or °F), the sensor's mV
signal, or the 4-20 mA instrument output.
Abbreviated identifiers are shown along with their related
numerical values to provide understandable readouts for
instrument setup, calibration and process monitoring. Pro-
cedure messages prompt the operator during instrument
setup and calibration. System diagnostic error messages
flash whenever the instrument detects an out-of-range input
for pH and/or temperature or a memory loss.
The 4-20 mA instrument output, which tracks the measured
pH, is isolated to eliminate problems caused by ground
loops. An output hold feature can be used to maintain the
latest output during calibration or instrument setup to sus-
pend operation of a receiving device. A range expand
feature allows the 4-20 mA output to represent a one pH
unit or larger segment of the measuring scale.
Modular construction simplifies field servicing and provides
electrical safety for the operator. The printed circuit module
assemblies contain voltages no greater than 24 VDC and
are safe to handle. A terminal strip compartment, with sepa-
rate access and weatherproof seals, permits electrical
hookup without exposing the instrument circuitry to the envi-
ronment.
A lithium battery on the backside of the display board re-
tains all user-entered setup values for approximately one
year (at 25°C), when loop power is removed. The battery's
capacity is one year of backup time which can occur over a
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