Operator`s manual

21X MICROLOGGER OVERVIEW
OV-3
OV1.2 SWITCHED EXCITATION OUTPUTS
The first four numbered terminals on the lower
terminal strip are the SWITCHED EXCITATION
channels. These supply programmable
excitation voltages for resistive bridge
measurements. The excitation channels are
only switched on during the measurement.
OV1.3 CONTINUOUS ANALOG OUTPUTS
The two Continuous Analog Output (CAO)
channels supply continuous output voltages,
under program control, for use with strip charts,
X-Y plotters, or proportional controllers.
OV1.4 DIGITAL CONTROL PORTS
The six DIGITAL CONTROL PORTS (0 or 5
volt states) allow on-off control of external
devices. These control ports have a very
limited current output (5 mA) and are used to
switch solid state devices which in turn provide
power to relay coils (Section 14.4).
OV1.5 PULSE COUNT INPUTS
The four PULSE COUNT INPUTS measure
contact closure, low level AC, or high frequency
pulse signals.
OV1.6 12 VOLTS AND GROUND
The +12 volt terminal provides a direct
connection to the 21X power supply. The +12
and ground terminals can be used to connect
an external 12 volt battery to the 21X to
maintain system power while changing internal
batteries or to provide power for extended
periods in the field.
OV2. MEMORY AND PROGRAMMING
CONCEPTS
The 21X must be programmed before it will
make any measurements. A program consists
of a group of instructions entered into a program
table. The program table is given an execution
interval which determines how frequently that
table is executed. When the table is executed,
the instructions are executed in sequence from
beginning to end. After executing the table, the
21X waits the remainder of the execution
interval and then executes the table again
starting at the beginning.
The interval at which the table is executed will
generally determine the interval at which the
sensors are measured. The interval at which
data are stored is separate and may range from
samples every execution interval to processed
summaries output hourly, daily, or on longer or
irregular intervals.
Figure OV2-1 represents the measurement,
processing, and data storage sequence in the
21X and shows the types of instructions used to
accomplish these tasks.
OV2.1 INTERNAL MEMORY
The 21X has 40,960 bytes of Random Access
Memory (RAM), divided into five areas. The
five areas of RAM are:
1. Input Storage - Input Storage holds the
results of measurements or calculations.
The *6 Mode is used to view Input Storage
locations to check current sensor readings
or calculated values. Input Storage defaults
to 28 locations. Additional locations can be
assigned using the *A Mode.
2. Intermediate Storage - Certain Processing
Instructions and most of the Output
Processing Instructions maintain
intermediate results in Intermediate
Storage. Intermediate storage is
automatically accessed by the Instructions
and cannot be accessed by the user. The
default allocation is 64 locations. The
number of locations can be changed using
the *A Mode.