www.miinet.com
Moore Industries-International, Inc.
- 120 -
User’s Manual
238-760-00K
May 2019
Functional Safety Dual Input Smart HART® Temperature Transmitter
STZ
SECTION 7
Analog Output
Fail Response:
The STZ output (AO) is a current output set at 4 to 20mA. The AO must be
set to fail low (fail high is a non fail-safe condition when power is lost).
The logic solver must be either configured to detect a ‘fail low’ condition for SIL1 applications
(anything less than 4.0mA is detected as a fault) or a `fail windowed’ condition for SIL2
applications (anything outside the 4-20mA range is detected as a fault).
Trimming:
AO trimming should be used with extreme care as this facility is allowed to trim the
AO accuracy by as much as 2% of the trimming point value. It is the user’s responsibility to
ensure that the safety application can tolerate this.
Loop Test and Input Simulation
During configuration/setup, HART and DTM configuration provide the capability to fix the AO to
a specific value or simulate Device Variables. It is important to clear all tests and simulations
before exiting configuration or the unit will not operate correctly.
Process Safety Time
Process safety time is the minimum time from the initiation of a hazardous event to the point
where the hazardous event is unavoidable. Any safety function designed to either prevent the
event or at least mitigate its effect must be capable of performing its specified safety function in a
time period very much less than the process safety time.
The STZ response time can vary based on the type and range of input sensor. It will also be
longer if the running average filter and/or output damping is increased. With default settings, the
STZ has a typical step response time (end to end) of 450msec for a single sensor and 650msec
for a dual sensor input. The maximum step response time for all sensor input types* is
1.4 seconds for a single sensor and 2 seconds for dual sensors. The total diagnostic test time of
the unit is 30 minutes.
* The running average filter is set to 1 and damping is set to 0.
Operation and Maintenance
Do not connect the USB communications cable to the STZ and do not attempt to configure the
unit (using DTM or HART) while the unit is performing its safety function.