Emerson manual Rosemount 848L, Reference Manual, 00809-0100-4696,Rev AA September

Reference Manual

00809-0100-4696, Rev AA September 2004

Rosemount 848L

PS - When the hardware input consists of a continuous train of pulses at a rate less than 500 PPS, a prescaler can be used to reduce the pulse rate to something that does not change faster than the equation evaluation rate. The function is PS (i, divisor) where ‘i’ is the channel number (1-8) and ‘divisor’ is the number of pulses to count before setting its output true for one equation evaluation cycle. The counter rolls over at ‘divisor’ and keeps counting. The user must assure that there is always at least one execution cycle with a false value from PS for every true value. If the pulse rate exceeds the divisor times two, then the function returns Bad status and optionally a PlantWeb alert can be sent. Only ten of these functions are available because they require storage for previous values.

DO - Channels 9-16 are zero unless set by configured DO or MDO function blocks. This allows a function block link to set the value from a remote function block output or HMI screen switch. The values may be referenced in equations by the DO (d) function. The range of ‘d’ is 1 to 8. To directly drive an output from an external device the Output Equation would reference DO(d).

NOTE

The value of DO can change during an evaluation cycle if the macrocycle evaluates the DO block. This may require referencing the DO value in a single equation to “save” its state.

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