Normal Mode - Omega Engineering OMB-CHARTSCAN 1400 User Manual

Configuration Aspects for Programmers

Normal Mode

ChartScan has the ability to reject noise resulting from AC line pick-up when an Average weight setting of 16 or
more measurements per line cycle is used. This noise rejection factor is important, as it allows for higher
accuracy. When an average weight setting of 32 or more is used, ChartScan is operating in a line cycle
integration manner and can provide readings for DC voltage, AC voltage, and thermocouple-based temperatures
at a rate of up to 44 channels per second. Noise filtering improves by selecting higher average weight settings;
but reduces the overall response time of the unit.
You can use the following formulas to compute the amount of time needed to acquire one scan.
For 60 Hz systems:
For 50 Hz systems:
To use the Normal scan mode, such that noise filtering (line cycle integration) is enabled, use the
commands, or use ChartView (see Chapter 4).
Example:
M#0
W#16
Note:
If noise resulting from AC voltage line pick-up is not a problem, you can set the system to average 1, 2, 4, or 8
line cycles per channel for faster scanning throughput (high-speed, multiple channel application). For example,
if the unit is configured to take 1 sample per channel, it will scan 147 channels per second.
Note: In regard to AC voltage measurements, ChartScan only supports AC voltages having an input signal
frequency which is an integer multiple of the AC line cycle. For this reason, sampling weights less than
32 can yield incorrect results.
To use the Normal scan mode for high-speed, multiple channel applications (when noise filtering is not needed)
use the and
M# W#
Example:
M#0
W#1
Note:
Reading inaccuracies can result if common mode voltages on adjacent channels are widely dissimilar. This is
due to inadequate settling time at the instrumentation amplifier when the unit is scanning between channels.
Settling time is defined as the time measured to a point at which a transient voltage value is within a specified
percentage of the final voltage value. Settling time is usually measured in nanoseconds. To eliminate these
inaccuracies, the settling time can be increase with use of the
API Command Reference.
B-4
Scan time = #channels x (#samples/channel + 12) x 520.83 µs
Scan time = #channels x (#samples/channel + 12) x 625.00 µs
'Select normal mode
'Select 16 samples over which to average
The number of samples in the above example could also be one of the following: 64, 128, or
256. However, using the weight of 256 will limit the number of active channels in an
acquisition to 122 due to hardware constraints.
commands, or use ChartView (see Chapter 4).
'Select normal mode
'Select 1 sample over which to average
The number of samples in the above example could also be one of the following: 2, 4, or 8.
command as described in Appendix A,
D#
Appendix B
and
M# W#
ChartScan User's Manual