Emerson manual Logic Transducer Block, Rosemount 848L, Reference Manual

Rosemount 848L

Reference Manual

00809-0100-4696, Rev AA September 2004

The 848L can force the outputs to a predetermined state in the event of a device malfunction.

The following procedure can be used to set the fail safe condition for each

output:

1.Set MODE_BLK.TARGET to OOS

2.For each Output "n" select the parameter OUT_n_CONFIG.FAIL_SAFE

3.Select False, True or Last Good Value

4.Set MODE_BLK.TARGET to AUTO

Latching

Most often the inputs are scanned and the logic equations processed at a rate greater than the macrocycle frequency. To be certain that positive or negative transitions are communicated, the inputs, equation results, and output values can be latched until read by the function blocks.

The following procedure is used to set the latching state of each input, equation or output:

1.Set MODE_BLK.TARGET to OOS

2.Select the appropriate parameter for either inputs, equations, or outputs:

a.Inputs use parameter MACRO_IN_LATCH

b.Outputs use parameter MACRO_OUT_LATCH

c.Equations use parameter MACRO_EQ_LATCH

LOGIC TRANSDUCER BLOCK

For each input, output or equation select either "Latch Positive Pulses" or "Latch Negative Pulses" or “disabled”.

Logic Equations

The 848L provides for 16 Logic Equations and 4 Output Equations. The Output Equations drive the hardware outputs. Each logic equation consists of up to 80 characters with a semicolon as the last character. The equations are evaluated at a nominal rate of 100msec. However this will vary based on the number and complexity of the equations used. The logic block consists of variables that are connected to the hardware I/O, obtain values or send values over the bus and internally calculated variables as shown in

Figure 3-1.

The value or state of the logic block variables can be communicated on the bus by assigning the appropriate channel number of a DI or MDI block. The DO variables can be set externally by assigning the appropriate channel number in a DO or MDO function block. The DO function blocks do not drive the outputs directly. The DO function block can drive the output by referencing the appropriate DO variable in the output equations.

3-10