Honeywell STT25D, Operator'S Manual

Page: 30 / 40

Smart Temperature Transmitter STT250 – Operator Manual 27
6. INDICATION METERS
6.1 Introduction
Integral meters are supplied already installed by the factory and provide a display of
the transmitter output. Table II selection _ _ M gives a 4-20 mA analog output on a
moving coil display to
±
2% accuracy. A diode fitted across the meter enables loop
continuity in the event of a moving coil failure. To ensure adequate loop power
availability in this event, add 0.7 V power supply to the loop in addition to 10.8 V for
the transmitter (i.e. 11.5 V minimum supply Volts).
Table II selection _ _ S is the Smart Meter with LCD which accepts either the Digital
DE or the 4-20 mA analog signal. Regardless of signal type, the Smart Meter displays
a large bargraph accurate to
±
3% and visible from 10 meters away. The 4 ½ digit
display shows the output in % of span or in engineering units (except with STT25H
HART). With the 4-20 mA signal, this digital display is accurate to
±
0.5% of span.
With the Digital DE signal, the display has no error; displaying the digital output
exactly within its resolution of
±
0.05% for a
±
199.9 reading range,
±
0.5% for a
±
1999
reading range and
±
5% for a
±
19990 reading range.
The Smart Meter includes various status message and engineering unit information on
the LCD screen.
The Smart Meter obtains its power in series with the transmitter and requires
2.25 V power supply in addition to the transmitter’s 10.8 V (i.e. 13.05 V minimum
supply Volts). The minimum loop operating current is <3.8 mA.
6.2 Connection Information
The addition of a meter changes the user wiring connections, because a serial
connection of the meter in the negative 4-20 mA signal line from the transmitter is
required. Wire the meter as shown in Figure 14.
0 % 100
RED
YEL
BLUE
10V
RED
DIODE
WIRING FOR ANALOG METER
WIRING FOR SMART
METER
YEL
46188461-201
Figure 14: Meters Connections