Campbell Scientific SDM-SW8A 8-Channel Switch Closure Input Module - Manual (Page 12)

SDM-SW8A Switch Closure Input Module
The syntax of this instruction is as follows:
SDMSpeed ( BitPeriod )
The BitPeriod argument can be an integer or a variable. If the SDMSpeed
instruction is not in the program, a default bit period is used. If 0 is used for
the argument, the minimum allowable bit period is used. Table 5 shows the
default, minimum allowable, and maximum bit period for each of our CRBasic
dataloggers.
TABLE 5. Bit Period Values
Datalogger Default
Bit Period Minimum Allowable
Bit Period Maximum
Bit Period
CR800, CR850 26.04 μsec 8.68 μsec 2.2 msec
CR1000 26.04 μsec 8.68 μsec 2.2 msec
CR3000 26.04 μsec 8.68 μsec 2.2 msec
CR5000 30 μsec 8 μsec 3 msec
The equation used to calculate the bit rate depends on the datalogger used.
The datalogger will round down to the next faster bit rate.
Equation for CR800, CR850, and CR1000:
bit_rate=INT((k*72)/625)*Resolution
Where:
k= the value entered in BitPeriod
Resolution=8.68 microseconds
Equation for CR3000:
bit_rate=INT((k*144)/625)*Resolution
Where:
k= the value entered in BitPeriod
Resolution= 4.34
μsec.
Equation for CR5000:
bit_rate=INT(k*20)*Resolution
Where:
k= the value entered in BitPeriod
Resolution=50 nsec.
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