Campbell Scientific CR7 Measurement and Control System - Manual (Page 44)

SECTION 3. INSTRUCTION SET BASICS
3-2
Even though this display is the same as that
indicating an indexed input location, (Section
3.4) there is no indexing effect on excitation
voltage.
3.4 INDEXING INPUT LOCATIONS
When used within a Loop, the parameters for
input locations can be Indexed to the loop
counter. The loop counter is added to the
indexed value to determine the actual input
location the instruction acts on. Normally, the
loop counter is incremented by one after each
pass through the loop. Instruction 90, Step
Loop Index, allows the increment step to be
changed. See Instructions 87 and 90, Section
12, for more details.
To index an input location (4 digit integer), key
C after keying the value but before entering the
parameter. Two minus signs (-) will be
displayed to the right of the parameter.
3.5 VOLTAGE RANGE AND
OVERRANGE DETECTION
The RANGE code parameter on Input/Output
Instructions is used to specify the full scale
voltage range of the measurement and the
integration period for the measurement (Table
3.5-1).
Select the smallest full scale range that is
greater than or equal to the full scale output of
the sensor being measured. Using the smallest
possible range will result in the best resolution
for the measurement.
Two different integration sequences are
possible. The slow integration, 16.67
milliseconds, is one 60 Hz cycle and rejects
noise from 60 Hz AC line power as well as
having better rejection of random noise than the
fast integration. A PROM with 50Hz rejection is
available for countries whose electric utilities
operate at 50 Hz (Appendix B).
When a voltage input exceeds the range
programmed, the value stored is the maximum
negative number, displayed in the *6 Mode as
-99999. In output data from Final Storage, this
becomes -6999 in low resolution or -99999. in
high resolution.
An input voltage greater than +8 volts on one of
the analog inputs will result in errors and
possible overranging on the other analog inputs.
Voltages greater than 16 volts may permanently
damage the CR7.
TABLE 3.5-1. Input Voltage Ranges and Codes
Range Code Full Scale Range Resolution*
Slow Fast
16.67ms 250µs
Integ. Integ.
1 11 ±1500 microvolts 50 nanovolts
2 12 ±5000 microvolts 166 nanovolts
3 13 ±15 millivolts 500 nanovolts
4 14 ±50 millivolts 1.66 microvolts
5 15 ±150 millivolts 5 microvolts
6 16 ±500 millivolts 16.6 microvolts
7 17 ±1500 millivolts 50 microvolts
8 18 ±5000 millivolts 166 microvolts
*Differential measurement, resolution for single-ended measurement is twice value shown.
3.6 OUTPUT PROCESSING
Most Output Processing Instructions require
both an intermediate processing operation and
a final processing operation. For example,
when the Average Instruction, 71, is executed,
the intermediate processing operation
increments a sample count and adds each new
Input Storage value to a cumulative total
residing in Intermediate Storage. When the
Output Flag is set, the final processing
operation divides the total by the number of