Campbell Scientific CR7 Measurement and Control System - Manual (Page 13)

CR7 MEASUREMENT AND CONTROL SYSTEM OVERVIEW
OV-3
CR7
RE LIE F VA LV E
CAUTION PR ES S BU TT ON
BE FO RE
UN LO CK IN G CA SE
FIGURE OV1-1. CR7 Measurement and Control System
OV2. MEMORY AND PROGRAMMING
CONCEPTS
The CR7 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
CR7 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
CR7 and shows the types of instructions used
to accomplish these tasks.
OV2.1 INTERNAL MEMORY
The CR7 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.