4-20 mA & Serial Data Output Transmitter
for Resistance in Ohms
Exceptional accuracy at high update rates.
DIN Rail mounted, digitally programmable.
- 4-20 mA, 0-20 mA, 0-10V or -10V to +10V transmitter output, 16 bits, isolated
- RS232 or RS485 serial data output, Modbus or Laurel ASCII protocol, isolated
- Dual 120 mA solid state relays for alarm or control, isolated
- Five precalibrated resistance input ranges from 20.000 Ω to 200.00 kΩ
- Optional fixed 2 MΩ input range
- 1 mΩ resolution on 20 Ω scale
- Custom curve linearization for changing resistance transducers
- 2, 3 or 4-wire connection with lead resistance compensation
- Analog output resolution 0.0015% of span (16 bits), accuracy ±0.02% of span
- DIN rail mount housing only 22.5 mm wide, detachable screw-clamp connectors
- Universal 85-264 Vac / 90-300 Vdc or 10-48 Vdc / 12-32 Vac powerr
The Laureate Resistance Transmitter is factory calibrated for five jumper selectable resistance ranges from 20 Ω to 200 kΩ. A fixed 2.0000 MΩ range is also available as a factory special. Accuracy for all ranges is an exceptional 0.01% of full scale ±2 counts. Resolution is one part in 20,000. In the 20 Ω range, resolution is 1 mΩ, making the transmitter suitable for contact resistance and conductance measurements.
Transmitter connections can be via 2, 3 or 4 wires. With 4-wire hookup, 2 wires are used for excitation and two separate wires are used to sense the voltage across the resistance to be measured, thereby eliminating any lead resistance effects. With 3-wire hookup, the transmitter senses the combined voltage drop across the RTD plus two excitation leads. It also senses the voltage drop across one excitation lead, and then subtracts twice this voltage from the combined total. This technique effectively subtracts the lead resistance if the excitation leads are the same.
All resistance ranges are digitally calibrated at the factory, with calibration factors stored in EEPROM on the signal conditioner board. This allows ranges and signal conditioner boards to be changed in the field without recalibrating the transmitter. If desired, the transmitter can easily be calibrated using external standards plus scale and offset in software.
High read rates at up to 60 or 50 conversions per second while integrating the signal over a full power cycle are ideal for high-throughput manufacturing processes. Peak and valley values are automatically captured and may be displayed via a front panel pushbutton command or a control signal at the rear connector, or be transmitted as serial data.
Custom curve linearization, available with the Extended version, makes this transmitter ideal for use with transducers whose output is a changing resistance.
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.
- 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).
|±0.01% of range|
± 2 counts
Update Rate, Max
|16 bits (65,536 steps)
±0.01% of full scale ± 2 counts
50/sec at 50 Hz, 60/sec at 60 Hz
|Analog Output (standard)
| Output Levels
Compliance at 20 mA
Compliance at 10V
|4-20 mA, 0-20 mA, 0-10 Vdc, -10 to +10Vdc (user selectable)
10V (0-500Ω load)
2 mA (5 kΩ load or higher)
16 bits (65,536 steps)
0.02% of output span plus conversion accuracy
250V rms working, 2.3 kV rms per 1 minute test
|Serial Data Output (standard)
|RS232 or RS485 (half or full duplex), jumper selectable
300, 600, 1200, 2400, 4800, 9600, 19200 baud
250V rms working, 2.3 kV rms per 1 min test
Modbus RTU, Modbus ASCII, Laurel ASCII
Modbus over Serial Line Specification V1.0 (2002)
RJ45 jack for 10/100Base-T Ethernet cable
Screw terminals for easy daisy chaining
247 for Modbus, 31 for Laurel ASCII
|Dual Relay Output (standard)
| Relay Type
| Two solid state relays, SPST, normally open, Form A
120 mA at 140 Vac or 180 Vdc
Low Power Option
|85-264 Vac or 90-300 Vdc (DC operation not ETL certified)
10-48 Vdc or 12-32 Vac
DC or 47-63 Hz
250V rms working, 2.3 kV rms per 1 min test
2W typical, 3W with max excitation output
|129 x 104 x 22.5 mm case
35 mm rail per DIN EN 50022
Plug-in screw-clamp connectors
|0°C to 55°C
-40°C to 85°C
95% at 40°C, non-condensing
Mount transmitters with ventilation holes at top and bottom.
Leave 6 mm (1/4") between transmitters, or force air with a fan.
|Resistance Measurements with Excitation & Lead Compensation|
||Ohm transmitter hookup can be via 2, 3 or 4 wires to the J5 connector. The transmitter applies a fixed excitation current for each resistance range.
In 4-wire hookup, different pairs of leads are used to apply the excitation current and sense the voltage drop across the unknown resistance, so that the IR drop across the excitation leads is not a factor.
||In 3-wire hookup, the transmitter senses the combined voltage drop across the unknown resistance plus two excitation leads. It also senses the voltage drop across one excitation lead, and then subtracts twice this voltage from the combined total. This technique effectively subtracts all lead resistance and compensates for ambient temperature changes if the two excitation leads are identical.
||In 2-wire hookup, the transmitter senses the combined voltage drop across the unknown resistance and both lead wires. The voltage drop across the lead wires can be measured by shorting out the resistance during transmitter setup, and this voltage is then automatically subtracted from the combined total. However, changing resistance of the lead wires due to ambient temperature changes will not be compensated.
QA Application with Relays in Passband Mode
||A deviation limit (50 mΩ in this example) is set up around both sides of a setpoint. The relay closes (or opens) when the reading falls within the deviation band, and opens (or closes) when the reading falls outside of this band. This mode sets up a passband around the setpoint and can be used for contact resistance testing in a production environment.
Laureate Resistance Transmitter
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