Load Cell & Microvolt Input 4-20 mA Current Transmitter

Laureate 4-20 mA output, load cell or microvolt input transmitters are 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 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.

Two output ranges are user selectable: 4-20 mA or 0-10V. Output isolation from signal and power grounds is provided by a separate on-board power supply, which can drive 20 mA into a 600 ohm load for 12V compliance. Output isolation eliminates problems caused by ground loops.

In most applications, output resolution and accuracy will be limited by the 12-bit digital to analog converter (DAC), which provides 4096 output levels, or steps equal to 0.025% of output span. These are 5 µV for 4-20 mA or 2.5 µV for 0-10V. Accuracy is ±0.05% of output span.

The transmitters are housed in a DIN rail case that is only 22.5 mm (0.89") thick. Signal connections are via detachable screw-clamp plugs.

Built-in Load Cell Excitation

A built-in, isolated, 10V, 60 mA excitation supply can power up to two 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 supply variations. With 6-wire load connection, it also compensates for variation in resistance of the transducer leads, thereby allowing long cable runs.

Fast Read Rate

All Laureate analog input meters and transmitters use Concurrent Slope (Pat 5,262,780) analog-to-digital conversion, which allows up to 50 or 60 conversions per second, while integrating the signal over a full power line cycle. High read rate is ideal for peak capture and for real-time computer interface and control.

Selectable Signal Filtering

The internal digital readings and analog output can be separately selected to be either unfiltered or filtered.

• An unfiltered selection updates after each conversion for fastest response, up to 60/sec, while integrating the input signal over a full power cycle. Fast read rate provides true peak 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. Another choice is Auto, which provides an automatic time constant selection based on the signal noise characteristics.

Easy Setup & Scaling

Transmitter programming is via a three-terminal RS-232 port using Laurel's PC-based Instrument Setup Software. This software can be downloaded from this website at no charge. The required transmitter-to-PC interface cable is available from Laurel (P/N CBL03). Scale and offset can be set by either of two methods:

• With the coordinate reading method, the Laureate reads the high and low signal values, and the user enters the desired high an low reading values. The Laureate then calculates the span multiplier and offset. This method is ideal if an external calibration reference is available.
   

• With the manual coordinate method, the user enters the high and low input values in Volts plus the desired high and low reading values. This method is suitable if no external calibration reference is available.