ABB TTH300 - Safety Function

Safety function
SM/TTX200/TTX300/SIL-EN TTH200, TTR200, TTH300, TTF300, TTF350 9
6 Safety function
TTH200-.H, TTR200-.H, TTH300-.H, TTF300-.H, and TTF350-.H transmitters generate a linear
temperature unit signal of 4 ... 20 mA. All safety functions refer strictly to the analog output
signal.
The entire valid range for the output signal must be configured between min. 3.8 mA and max.
20.5 mA (factory setting).
Warning!
In safety mode, HART communication occurs only when write protection is activated. The
HART master must comply with the safety requirements of the customer application.
Alarm behavior and current output
When a critical error is detected, the configured alarm current is generated and fed to a
downstream logics unit (a DCS, for example), which checks for overshoots of a defined
maximum value. There are two selectable modes for this alarm current:
• HIGH ALARM (high alarm, maximum alarm current); this is the factory setting
• LOW ALARM (low alarm, minimum alarm current)
The low alarm current can be configured in a range from 3.5 … 4.0 mA. The factory setting is
3.6 mA.
The high alarm current can be configured in a range from 20.0 … 23.6 mA. The factory setting
is 22 mA.
In the following cases, a detected error is displayed independently of the configured alarm
current within the low alarm range:
• Runtime errors
• Memory error (non-volatile data, RAM, ROM)
After switching on or restarting the transmitter electronics unit, the minimum low alarm time
(LOW alarm, startup time) is 10 to 15 seconds.
Warning!
To ensure accurate error monitoring, the following conditions must be fulfilled:
• The low alarm must be configured to a value ≤ 3.6 mA.
• The high alarm must be configured to a value ≥ 21 mA.
• The DCS must identify the configured high and low alarms as malfunctions, and the alarm
must be configured accordingly.
Warning!
To ensure reliable functioning of the current output, the terminal voltage at the device must be
between 11 V and 42 V DC (non-hazardous-area design) and 11 V and 30 V DC (hazardous
area design).