MA1044 MAQ20-RTD31/-RTD41 Hardware User Manual
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14.0 Channel Scan Rate, System Throughput & Module Internal Multiplexer
MAQ20-RTD31 and MAQ20-RTD41 modules internally multiplex the 6 channels of the MAQ20-
RTD31 and the 5 channels of the MAQ20-RTD41 to a high performance, programmable gain,
instrument amplifier. Enabled channels specified by the Channel Enable register, as shown in the
Range Selection, Channel Enable & Reading Signals
section, are continuously scanned, filtered,
amplified, and fed to an analog-to-digital converter. Sampled data is then stored in local memory and
accessed using the Channel Data registers as shown in shown in the
section. As new data is acquired, previous sampled data is overwritten
such that local memory always has the most recent data. The module internal multiplexer operates
at a fixed rate of 5ms/Ch. When a channel data read command is received, data for all channels is
retrieved from local memory and returned in a single response. A standard command-response cycle
takes 6ms. Channel scan rate at the system level depends on the number of MAQ20 I/O modules
installed in a system. As more modules are added to a system, each is scanned sequentially,
therefore the scan rate for an individual module and for the channels within that module decreases.
The following calculation is used to determine channel scan rate for each of the 6 input channels in
a MAQ20-RTD31 input module operating in a system of modules. The same method applies to
determine the channel scan rate of the 5 input channels in a MAQ20-RTD41 module.
Command-response cycle = 6ms
Module Scan Rate = Number of MAQ20 I/O modules in a system/6ms Scans/s
During each command/response cycle, 6 channels of data are acquired. The net scan rate is then:
Net Scan Rate = Module Scan Rate * Number of channels
Example:
Determine the rate at which data can be acquired from channels in the MAQ20-RTD31
module if the module is in the following system:
MAQ20-COM4
MAQ20-RTD31
The scan rate for each of the input channels is the same as the scan rate for the module in the
system:
Scan Rate, Channels 0 through 5 = 1/6ms = 167 Scans/s = 167Hz
During each command/response cycle, 6 channels of data are acquired. The net scan rate is then:
Net Scan Rate = 167Hz * 6 channels = 1002 Ch/s
Example:
Determine the rate at which data can be acquired from channels in the MAQ20-RTD31
module if the module is in the following system:
MAQ20-COM4
MAQ20-VDN
(8 channels)
MAQ20-ISN
(16 channels)
MAQ20-RTD31
(6 channels)
MAQ20-KTC
(8 channels)
MAQ20-RTD41
(5 channels)
MAQ20-MVDN
(8 channels)
The scan rate for each of the input channels is the same as the scan rate for the module in the
system:
