Analog output
The LST300 has a 4-20 mA analog output for
transmitting measurements and alarms.
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20 mA output and power input are
transmitted on the same wire.
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The output current is a process variable
under normal conditions. It can also be
used as fault protection or as a fixed
value to indicate the alarm situation.
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Low alarm value can be configured in the
range of 3.5 mA - 3.6 mA.
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The high alarm value can be configured in
the range of 21 mA - 22.6 mA.
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The refresh frequency of 4 - 20 mA output is
0.2 seconds.
HART Communication
HART protocol is used for digital communication
between process control system/PC, handheld
terminal equipment and LST300. It can be used to
send all equipment and measurement point
parameters from transmitter to process control
system or PC.
It also provides a way to reconfigure the
transmitter. Digital communication utilizes
alternating current (4 - 20 mA) superimposed on
analog output, without affecting any instrument
connected to the output.
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HART communication and power are
transmitted on the same cable. No
additional cables are required.
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HART communication requires an
additional resistor.
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The minimum resistance of the resistor is
250 ohms. Resistors on power lines can
cause voltage drop, which should be
considered to ensure that the supply
voltage for LST300 is higher than the
minimum rated input voltage.
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The baud rate of HART communication is
1200.
Ground Connection
The LST300 needs to be grounded at the terminals,
as shown in Fig. 2.
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LST300 has two ground connectors (PE).
Effective grounding connection is needed
to achieve optimal EMC protection.
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If LST300 is used in hazardous
environments (Zone 1 and Zone 1 and Zone
2), all grounding must comply with
explosion-proof requirements.
Terminal connection example
Fig. 3 Electrical Connection - HART Version
1. Power Supply
2. Remote Display
3. Handheld Terminal Equipment
4. External grounding connection
5. Internal grounding connection
6. Cable entrance
Explosion-proof transmitters
must be repaired by the
manufacturer or approved by
qualified technical experts after
repair. Please observe the
relevant safety precautions
before, during and after the
repair work.
Warning