Campbell Scientific CR9000X Measurement and Control System - Manual (Page 257)

Section 7. Measurement Instructions
7-33
SDMTrigger
When SDMTrigger is executed, the CR9000X sends a "measure now" group
trigger to all connected SDM devices. SDM stands for Synchronous Device
for Measurement. SDM devices make measurements independently and send
the results back to the datalogger serially.
The SDMTrigger instruction allows the CR9000X to synchronize when the
measurements are made. Subsequent Instructions communicate with the SDM
devices to collect the measurement results. Not all SDM devices support the
group trigger; check the manual on the device for more information.
SDMX50 (SDMAddress, Channel)
SDMX50 allows individual multiplexer switches to be activated independently
of the TDR100 Instruction.
SDMX50 is useful for selecting a particular probe to troubleshoot or to
determine the apparent cable length.
Because it is usually easy to hear the multiplexer(s) switch, the SDMX50
instruction is a convenient method to test the addressing and wiring of a level
of multiplexers: Program the datalogger to scan every few seconds with the
SDM address for the multiplexer(s) and channel 8.
The Instruction always starts with channel 1 and switches through the channels
to get to the programmed channel. Switching to channel 8 will cause the most
prolonged noise.
Remember each multiplexer level has a different SDM Address. Level 1
multiplexers should be set to the address 1 greater than the TDR100, Level 2
multiplexers should be set to the address 2 greater than the TDR100 and Level
3 multiplexers should be set to the address 3 greater than the TDR100. If the
SDMX50 multiplexers for a given level are connected and have their addresses
set correctly they should all switch at the same time.
Parameter
& Data Type Enter
SDMAddress
Constant The SDMAddress of the SDMX50 to switch. Valid SDM addresses are 0
through 14.
Channel
Constant The SDMX50 channel to switch to (1-8)