Measurement Computing TempScan/1100 - Manual (Page 61)

TempScan / MultiScan User's Manual 879596 System Configuration 4-3
Note: (1) For DC voltage and temperature, the term averaging implies obtaining the average
measurement over the specified number of samples. (2) For AC voltage, the term averaging
implies computing the RMS (Root Mean Square) value over the specified number of samples.
To Compute the MultiScan/1200 Scan Interval
To compute the time interval for the MultiScan/1200 to acquire one scan, use the following formulas:
• For a 60-Hz Line Cycle: Scan Interval equals:
Is-m = Cv x (Wv + 12) x R1
• For a50-Hz Line Cycle: Scan Interval equals:
Is-m = Cv x (Wv + 12) x R2
Where:
Is-m = Scan Interval for the MultiScan/1200, milliseconds.
Cv = Channels, variable number of configured channels in the scan.
Wv = Sampling Weight, variable number of samples per channel.
R1 = Sampling Rate, constant of 0.52083 milliseconds per sample for a 60-Hz line cycle.
R2 = Sampling Rate, constant of 0.62500 milliseconds per sample for a 50-Hz line cycle.
To compute the time interval for the TempScan/1100 to acquire one scan, see section To Compute the
TempScan/1100 Scan Interval.
Line-Cycle Integration / High-Speed Multi-Channel Mode
The ability of the MultiScan/1200 unit to sample and average 32 measurements per line cycle enables it to
reject noise resulting from AC line pickup, hence making it useful for high-accuracy applications. When in
line-cycle integration / high-speed multi-channel mode with the default weight of 32 samples per channel,
the unit can provide AC voltage, DC voltage, and thermocouple readings at a rate of up to 44 channels per
second. Further noise filtering is available with averaging over 2, 4, or 8 line cycles (at 32 samples per line
cycle) by selecting a weight of 64, 128, or 256 samples, respectively.
Sampling Weight Options
Weight (wt) Line Cycles (32 Measurements Each) Maximum Number of Channels
1,2,4,8,16,32 1 744
64 2 431
128 4 234
256 8 122
CAUTION
Due to hardware constraints, weights greater than 32 (default) limit the number of
channels which can be active in an acquisition.
If noise resulting from AC line pickup is not a concern, you can program the MultiScan/1200 unit to
average 1, 2, 4, 8, or 16 samples per channel for faster scanning throughput. For example, using the scan
interval formula for a 60-Hz line cycle, if the unit is configured to take 1 sample per channel, it can scan
147 adjacent channels per second. This means a fully-expanded MultiScan/1200 system could scan all of
its 744 channels every 5 seconds.