4-20 mA Current Output Transmitter for Strain Gauge & Potentiometer Input

The Laureate 4-20 mA output, 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 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.

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 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 at up to 50 or 60 conversions per second while integrating the signal over a full power line cycle is provided by Concurrent Slope (Pat 5,262,780) analog-to-digital conversion. High read rate is 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. 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 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. Another choice is Auto, which provides an automatic time constant selection based on the signal noise characteristics.

Three analog transmitter settings are jumper selectable: 4-20 mA, 0-20 mA or 0-10V. All selections provide 16-bit (0.0015%) resolution of output span and 0.02% output accuracy. The output tracks the reading from -99,999 to +99,999 counts that would be transmitted digitally. For DC signals, this reading has a rated accuracy of ±0.01% of full scale input and can be scaled in software. Output isolation from signal and power grounds eliminates potential ground loop problems. The supply can drive 20 mA into a 500 ohm (or lower) load for 10V compliance, or 10V into a 5K ohm (or higher) load for 2 mA compliance.

• Analog transmitter output, 16-bit, user scalable and isolated. User selectable 4-20 mA, 0-20 mA or 0-10V levels.
• Serial communications, isolated. User selectable RS232 or RS485, half or full duplex, Modbus or Laurel ASCII protocol.
• Dual solid state relays for control or alarm, isolated. Rated 120 mA at 130 Vac or 170 Vdc.
• Transducer excitation output, isolated. User selectable 5V@100 mA, 10V@120 mA or 24V@50 mA.
• Universal AC power supply for 85-264 Vac.

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).