4-20 mA & Serial Data Transmitter for Load Cell & Microvolt Signals

The Laureate load cell or microvolt input transmitter is designed for use with load cells, strain gauges and microvolt input signals where exceptional sensitivity and stability are required. A most sensitive full-scale input range ±20.000 mV can be scaled internally to ±99,999 counts. The selected input range for the full 0-20 mA output span can be as wide as ±99,999 counts or as narrow as 150 counts, limited only by considerations of electrical noise and time constants of the programmable moving average digital filter. The unit's serial data output is accurate to ±0.01% of reading ±2 counts in ratiometric load cell mode and ±0.01% of full scale in ±2 counts in absolute microvolt meter mode.

A built-in, isolated, 10V, 120 mA excitation supply can power up to four 350-ohm load cells in parallel. Load cell connection can be via 4 or 6 wires. With 4-wire load connection, the transmitter operates in a ratiometric mode to eliminate errors due to power supply variations. With 6-wire load connection, it also compensates for lead resistance, allowing long cable runs.

Fast read rate at up to 50 or 60 conversions per second while integrating the signal over a full power line cycle are ideal for peak or valley capture and for real-time computer interface and control.

Digital signal filtering modes are selectable for stable readings in electrically noisy environments.

• An unfiltered selection provides true peak and valley readings and aids in control applications.
• A batch average filter selection averages each 16 conversions for an update every 1/4 sec.
• An adaptive moving average filter selection provides a choice of 8 time constants from 80 ms to 9.6 s. When a significant change in signal level occurs, the filter adapts by briefly switching to the shortest time to follow the change, then reverts back to its selected time constant. An Auto setting selects the time constant selection based on signal noise.

Standard features of Laureate LT transmitters include:

• 4-20 mA, 0-10V or -10V to +10V analog transmitter output, isolated, jumper-selectable and user scalable. All selections provide 16-bit (0.0015%) resolution of output span and 0.02% output accuracy of a reading from -99,999 to +99,999 counts that is also transmitted digitally. Output isolation from signal and power grounds eliminates potential ground loop problems.
• Serial communications output, RS232 or RS485 (half or full duplex), jumper selectable. Three protocols are user selectable: Modbus RTU, Modbus ASCII, or Laurel ASCII. Modbus operation is fully compliant with Modbus Over Serial Line Specification V1.0 (2002). The Laurel ASCII protocol is simpler than the Modbus protocol and is recommended when all devices are Laureates.
• Dual solid state relays, isolated, for alarm or control. Rated 120 mA at 140 Vac or 180 Vdc.
• Transducer excitation output, isolated. User selectable 5V@100 mA, 10V@120 mA or 24V@50 mA.
• Universal 85-264 Vac power. Low-voltage 10-48 Vdc or 12-32 Vac power is optional.

Easy Transmitter programming is via Laurel's Instrument Setup Software, which runs on a PC under MS Windows. This software can be downloaded from this website at no charge. The required transmitter-to-PC interface cable is available from Laurel (P/N CBL04).

Load Cell Transmitter Connections

	In 4-wire connection, the excitation and sense lines are tied together. The transmitter can make ratiometric corrections for supply voltage variations, but does not compensate for variations in lead resistance. This connection is often used with short cable runs.
	In 6-wire connection, the sense lines are separate from the excitation lines, thereby eliminating effects due to variations in lead resistance. This allows long cable runs in outdoor environments with temperature extremes.
	For large scales, up to four 350 ohm load cells can be powered by a single Laureate, whose excitation output is rated 120 mA at 10V. The excitation and sense points of the four bridges are connected in parallel. The load cell outputs will be averaged if the load cells have the same sensititivity in mV/V.