Specifications

8 – Configuring Points
124 R400
Number of States
Status point PVs are used to represent the current “state” of the field device or
process. For example, you could define four distinct states for a valve: TRAVEL,
CLOSED, OPEN, and FAIL. The PV for a status point in PlantScape can be used to
represent up to eight discrete states.
When you define the main properties for a status point, you need to specify the
number of discrete input states you wish to represent with this point.
Status points represent these states by reading up to three consecutive discrete
values from an address in the controller. If you need to monitor one or two states,
you need a 1-bit address; for three to four states, it will be 2-bit; and for five to
eight states it will be 3-bit.
Note • Bits are numbered from the least significant to the most significant.
• For 2- and 3-bit addresses, the bits are assumed to be contiguous.
State Descriptors
For each state you wish to use, you need to define a short alphanumeric
descriptor. The number of descriptors you enter must match your selected
number of states.
For example, if you wanted to use a point to monitor and control a valve, the PV
might be used to represent 4 states of that valve and the descriptors might be:
TRAVEL, CLOSED, OPEN, and FAIL.
Figure 8.2 Status Point Configured for Eight States
INVALID
INVALID
INVALID
INVALID
LOW
MEDI UM
HIGH
7
6
5
4
3
2
1
0
3-Bit Binary
Value “111”
Status Point PV
ServerField Controller
Level Switch
HIGH Level
EMPTY
MEDIUM
LOW
Digital Inputs
plscpcg.book Page 124 Monday, May 28, 2001 10:11 AM