Campbell CR23X, Руководство оператора

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SECTION 9. INPUT/OUTPUT INSTRUCTIONS
9-13
If the excitation channel is indexed, parameter 4
becomes an input location. The excitation
voltage must be loaded into the specified input
location before Instruction 22 is executed.
PARAM. DATA
NUMBER TYPE DESCRIPTION
01: 2 Excitation channel
number (Table 9-2A)
02: 4 Delay time in
hundredths of a second
that excitation is on
03: 4 Delay time in hundredths
of a second after
excitation is turned off
04: 4 Excitation voltage in
millivolts/Input location
Input locations altered: 0
*** 23 BURST MEASUREMENT ***
FUNCTION
Instruction 23 will repeatedly make a voltage
measurement on a series of single-ended or
differential channels, applying excitation if desired.
The measurement units are millivolts prior to
scaling. The measurements saved can be those
made immediately upon execution of the
instruction or grouped around a specified trigger
condition. The results of the measurements may
be stored in Input Storage or the raw A/D data can
be sent out the serial port. The minimum sample
interval per channel is .667 ms (i.e., one channel
can be sampled at a maximum rate of 1.5 kHz).
CAUTION: Measurement accuracy
specifications will not be met on the
±
10 mV
input range when the sample interval per
channel is set lower than 1 ms because of
insufficient settling time.
MEASUREMENT
The voltage measurement uses the fast
integration time of 250
µ
s. Differential
measurements are made with a single
integration. The input settling time before an
integration is 370
µ
s for intervals greater than or
equal to 1 ms per channel and 100
µ
s for
intervals less than 1 ms per channel. The short
100
µ
s input settling time was chosen to allow
burst measurements up to 1.5 kHz, at the
expense of adequate input settling time on the
±
10 mV input range. The
±±±±
10 mV input range
will not meet the specified measurement
accuracy for intervals less than 1 ms per
channel.
Settling errors on the order of
±
100
µ
V were measured with a 1 k
Ω
source
impedance when using less than 1 ms per
channel in the burst mode. Settling errors are
worsened for sensors with long leads and/or
high output impedance. See Section 13.3 for
discussion of settling time and time constants.
Excitation is always supplied from excitation
channel 1. The excitation voltage in millivolts is
entered in Parameter 9. If excitation is not
desired, enter 0 for Parameter 9.
Three options are available for the first digit in
Parameter 4.
0 - Trigger on first measurement channel.
1 - Trigger on Digital Control Port 1.
2 - Trigger on first measurement channel, set
Digital Control Port high when trigger is met
and low when measurements have finished.
When triggering on options 0 or 2, the
measurement on the first specified channel
(Parameter 3) is compared to the limit specified
in Parameter 8. The user's multiplier and offset
are not applied before the comparison: the limit
must be entered in units of millivolts. If a digital
trigger (low < 1.5V, 3.5 V < HIGH < 5 V) is used,
it must be input to Digital Control Port #1.
Option 2 is useful when 2 or more CR23X's are
required to start "Bursting" at the same time.
For example, Digital Control Port #1 of all the
CR23X's involved are connected in parallel.
The master CR23X sets its Digital Control Port
#1 high when the trigger condition is met. The
remaining dataloggers, programmed with option
1, trigger on the digital signal. The master
CR23X sets Port #1 low when its
measurements are completed.
Five trigger options are available for the second
digit in Parameter 4:
0 trigger immediately,
start saving or sending data with the first
measurement made;
1 trigger if the
measurement is greater than the limit entered
or if the digital trigger is high;
2 trigger if the
measurement is less than the limit or if the
digital trigger is low;
3 trigger on rising edge;
i.e., when the measurement goes from below to
above the limit or when the digital trigger goes
from low to high;
4 trigger on falling edge; i.e.,
trigger when measurement goes from above the
limit to below it or when the digital trigger goes
from high to low. When triggering on the rising
or falling edge, the input must make the