Flowserve UEX Limitorque - Manual (Page 25)

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Limitorque UEX FCD LMENIM1205-03-AQ – 05/15
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6.5 Remote External Interlocks/Inhibits
Three user-defined inputs are provided for the connection of remote contacts that will prevent motor-
ized operation of the actuator. These are effective in both Remote and Local modes and may only be
overridden by a maintained ESD signal, if so configured (refer to Figure 15.1 for wiring connections).
For ESD connections, the user may select either a single common or isolated commons.
6.6 Absolute Position Encoder
An absolute position encoder, incorporated into the L120 actuators, is the same as the encoder used in the
MXa. It includes 18 phototransistors that are switched on and off by a gear/wheel mechanism.Valve position
is sensed by an 18-bit, optical, absolute position encoder with redundant position sensing circuits designed
for Built-In Self-Test (BIST).
Each of the position sensing circuits is redundant, facilitating BIST. The BIST feature discerns which
failures will signal a warning only and require a warning plus safe shutdown of the actuator. Open and
closed positions are stored in permanent, nonvolatile memory. The encoder measures valve position at
all times, including both motor and handwheel operation, with or without power present, and without the
use of a battery. The absolute encoder is capable of resolving ±7° of output shaft position and over 10,000
output drive rotations, however, in the L120, the encoder is limited to the maximum geared limit switch
travel. Refer to Table 3.1.
This design permits continuous monitoring of valve position during motor and handwheel operation. The
encoder is 100% repeatable and requires no backup power source for operation. The output is used to
control the open and closed valve position and measure and report valve position, as well as provide local
and remote position feedback.
The positioning accuracy is better than 99% for valves requiring 50 or more turns. For the maximum
actuator turns and resolution, see Table 3.1.
Figure 6.2 – Absolute Position Encoder
18-bit optical, redundant position
encoder provides continuous valve
position monitoring without battery
backup with Built-In Self-Test (BIST)
capabilities.