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Appendix C — Bi-Phase Mark Implementation
Varec, Inc. 177
Appendix C — Bi-Phase Mark Implementation
This protocol chapter explains the operation of the Bi-Phase Mark as it pertains to the 2920
Float & Tape Transmitter.
Implementation
The implementation of the Bi-Phase Mark (BPM) protocol on the 2920 supports a variety of
commands represented by a TOR (Type of Request) and some of them further by an item. All
of them are defined by an ASCII character on the request frame.
The Bi-Phase Mark functions implemented in the 2920 FTT are listed in the table below.
TOR Item Description
A Alarm Status Record
B Alarm Status and Level Record
C Alarm Status and Temperature Record
D Alarm Status, Level, and Temperature Record
L Alarm Status and Level Record
Z AF Analog Output Overwrite
With this item, the user can manually overwrite the current output
through the Host interface.
AK Analog 1 Output Mode
This item determines under what conditions the analog output current
will operate.
Overwrite mode (Host can send output value): D, O & P
Level Output (Output follows a valid Tank Level): L, M, A, B, I, and J .
AL Tank Level
Read current tank level.
AM Analog Output 4 mA value (Offset)
This item must be programmed with the level value which corresponds
with an output current of 4 mA.
AN Analog Output 20 mA value (Scale)
This item must be programmed with the level value which corresponds
with an output current of 20 mA.
HA High Alarm
If the tank level rises above the high alarm level, the relevant bit is set in
the Level status. This bit remains set until the displacer drops below the
high alarm level.
HH High High Alarm
High High Alarm sets the high-high alarm level. The monitoring of High
High is identical to the High Alarm.