LST300 | COMPACT ULTRASONIC LEVEL TRANSMITTER | LST300–EN REV. E
17
cba
Figure 19 Termination introduction
a Positive polarity of power supply (+)
b Negative polarity of power supply (-)
c Extend meter, shorted with negative polarity for normal use (Ext)
DC power supply
The LST300 operates from a DC power supply that is connected
to the terminals shown in Fig. 15.
• Open the blind cover first to connect the cable.
• The power supply voltage is 12 to 42 V DC without surge
protection, and 14 to 42 V with surge protection when the -
and Ext Meter terminals are shorted.
• It is recommended to use twisted pair cables for better
resistance to electrical disturbance.
Analog output
LST300 has a 4 to 20 mA analog output to transmit
measurements and alarms.
• The 4 to 20 mA output and power supply input share the same
wires.
• The output current is the process variable during normal
conditions. It can also be a fixed value as a failsafe or to
indicate alarm conditions.
• The current output range of a valid signal is 4 to 20 mA.
• The Low Alarm value is configurable in the range of 3.5 mA to
3.6 mA.
• The High Alarm value is configurable in the range of 21 mA to
22.6 mA.
• The refresh frequency of the 4 to 20 mA output is 0.2 second.
HART communications
The HART protocol is used for digital communication between a
process control system / PC, a handheld terminal, and LST300.
It can be used to send all device and measuring point
parameters from the transmitter to the process control system
or PC. Conversely, it also provides a means of reconfiguring the
transmitter. Digital communication utilizes an alternating
current superimposed on the analog output (4 to 20 mA) that
does not affect any meters connected to the output.
• The HART communication shares the cable with the power
supply. No additional wires are required.
• An extra resistor is needed for HART communication. The
minimum value of resistor is 250 ohm. The resistor in power
line causes voltage drop, and should be considered to ensure
the power supply to the LST300 remains above the minimum
rated input voltage.
• The baud rate of the HART communication is 1200.
Grounding
The LST300 requires a ground connection to the terminal as
shown in Fig. 16.
• The LST300 provides two connectors for ground (PE). An
effective ground connection is needed for optimum EMC
protection.
• All grounding must comply with anti-explosion regulations if
the LST300 transmitter is to be used in hazardous
environments (Zone 1 Div 1 and Zone 1 Div 2).
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