Laurel Electronics LAUREATE SERIES SCALE-WEIGHT METER - Manual (Page 4)

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3. PRODUCT INTRODUCTION
The Scale Meter is a compact, inexpensive, and extremely accurate digital panel meter with
special firmware for weighing applications. It is available with a load cell or a DC signal condi-
tioner board.
The load cell signal conditioner board accepts full-scale ranges of ±20, ±50, ±100, ±250
and ±500 mV with 4- or 6-wire load cell hookup to display up to 99,999 counts. With 4-wire
hookup, the meter operates in a ratiometric mode to eliminate errors due to supply variations.
With 6-wire hookup, it also compensates for variations in transducer lead resistance, thereby
allowing long cable runs in changing temperature environments. The built-in, isolated excita-
tion supply can power up to four 350-ohm load cells in parallel at 10 Vdc.
The DC signal conditioner board can be jumpered for ratiometric strain gauge voltage
ranges ±200 mV, ±2V or ±20V. With this board, a 20 mV strain gauge output can be scaled to
display up to 10,000 counts, while a 200 mV output can be scaled to display up to 99,999
counts.
Meter accuracy is 0.01% of full scale ± 2 counts. Custom curve linearization, available with an
optional Extended main board, can extend the accuracy of actual load cells near the low and
high ends of their ranges. It also allows high accuracy readings to be achieved with lower cost,
less linear load cells.
The standard power supply is a switching model designed for universal AC power. A low-
voltage supply is optional for power from 10-48V batteries or from 12-30 Vac. Both supplies
provide an isolated 5, 10 or 24Vdc transducer excitation output.
The meter case conforms to the 1/8 DIN size standard. It is made of high impact, 94V-0 UL-
rated plastic and is watertight to NEMA-4 (IP65) when panel mounted. Mounting is from the
front of the panel and requires less than 110 mm behind the panel. Power and signal wiring is
via removable plugs conforming to UL61010C safety standards. All output options are isolated
from meter and power ground to 250 Vac.
Alarm or setpoint control is provided by an optional relay board with two Form C 8A contact
relays or two Form A 130 mA solid state relays. The setpoints may be latching or non-latching,
be energized above or below the setpoint, or operate in a fail-safe mode. The relays can
operate from the filtered signal to reduce relay chatter or from the unfiltered signal for fastest
response. Snubber circuits and a programmable relay switching time delay extend relay
contact life.
An isolated analog output of 4-20 mA, 0-20 mA, 0-10V or -10 to +10V can be provided by an
optional analog output board. The output is linearized to the display and can operate from the
filtered or unfiltered signal input. It can be scaled via front panel pushbuttons or the meter’s
serial interface.
Ethernet, USB, RS232, or RS485 (2-wire half-duplex or 4-wire full-duplex) serial communi-
cations options are available with the Modbus protocol or a simpler custom ASCII protocol.
Modbus operation includes RTU or ASCII modes, up to 247 digital addresses, and up to 32
devices per RS485 line without a repeater. Ethernet-to-RS485 and USB-to-RS485 converter
boards allow a meter to be interfaced to a PC and to multiple meters on an RS485 network.
Scale meter programming can be via the meter’s front panel or a PC running Windows
based Instrument Setup Software (serial interface option required).