COSA Xentaur Xentaur HDT - Manual (Page 27)

HDT User’s Manual
page 20
Appendix B:HDT pin 3 timing diagrams
0
4
8
12
16
20
24
28
32
Time (sec)
power on
3V 0V 3V 0V 3V 0V 3V 0V
high impedance high impedance high impedance high impedance
Pin 3 timing diagrams for the 4 possible modes
Pin 3 MODES When in Digital Echo mode When in Fault Reporting
‡
mode
When in Alarm Relay mode When in Switch Monitor mode
Low Voltage TTL (0-3V) in RS-232 inverted data format, using HART protocol Active = Spacing = RS-232 Positive Voltage : PIN3=high ~3V Idle = Marking = RS-232 Negative Voltage : PIN3=low ~0V
High impedance when fault detected Has highest precedence over other simultaneous modes Low when no fault, has lowest precedence with other simultaneous modes
when neither alarm is triggered (measurement is between Low & High Alarms)
when measurement is above High Alarm when measurement is below Low Alarm
On the next HART message HDT pulls pin 3 to 3.3V with a 10K resistor
Response Code byte 2, bit 6 PIN 3: Float =0, Ground =1
idle
idle
data
Note:
‡
The Fault Reporting Mode can be utilized simultaneously with either the Digital Echo or Alarm Relay Modes.
However when a fault occurs the high impedance fault condition will override the other signaling.