4-20 mA & Serial Data Output Transmitter for Resistance in Ohms

The Laureate Resistance Transmitter is ideal for high-speed, high-accuracy resistance measurements in a production environment, such as contact resistance measurements. It is factory calibrated for five jumper selectable resistance ranges from 20.000 ohm to 200.00 kohm. Factory-special, fixed ranges of 2.0000 ohm or 2.0000 Mohm are also available. Accuracy is an exceptional ±0.01% of reading ± 2 counts. Resolution is one part in 20,000. In the 2 ohm range, resolution is 0.1 milliohm for contact resistance 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 suitable for use with transducers whose output is a non-linear changing resistance. Linearization is provided by curvilinear spline fits, and the reading can be scaled in software for user-selected engineering units of measure.

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).

Features

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 jumper-selectable resistance ranges of 20.000 ohm to 200.00 kohm
Fixed factory-special resistance ranges of 2.0000 ohm or 2.0000 Mohm
0.1 milliohm resolution on 2 ohm scale for contact resistance measurements
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 power

Specifications

Range	Resolution	Accuracy	Excitation Current ***
0-2.0000 Ω	0.1 mΩ	±0.01% of reading ± 2 counts	5 mA
0-20.000 Ω	1 mΩ		5 mA
0-200.00 Ω	10 mΩ		500 µA
0-2000.0 Ω	100 mΩ		50 µA
0-20000 Ω	1 Ω		5 µA
0-200.00 kΩ	10 Ω		500 nA
0-2.0000 MΩ	100 Ω		500 nA

*	Jumper-selectable, precalibrated range.
**	Factory-set fixed range.
***	The applied excitation current is sensed by the meter, which operates in a ratiometric mode and automatically compensates for any changes in excitation.

Signal Input
Input Resolution	16 bits (65,536 steps)
Input Accuracy	±0.01% of reading ± 2 counts
Update Rate, Max	50/sec at 50 Hz, 60/sec at 60 Hz
Analog Output (standard)
Output Levels	4-20 mA, 0-20 mA, 0-10 Vdc, -10 to +10Vdc (user selectable)
Compliance, 4-20 mA	10V (0-500Ω load)
Compliance, 0-10V	2 mA (5 kΩ load or higher)
Output Resolution	16 bits (65,536 steps)
Output Accuracy	0.02% of output span plus conversion accuracy
Output Isolation	250V rms working, 2.3 kV rms per 1 minute test
Serial Data Output (standard)
Signal Types	RS232 or RS485 (half or full duplex), jumper selectable
Data Rates	300, 600, 1200, 2400, 4800, 9600, 19200 baud
Output Isolation	250V rms working, 2.3 kV rms per 1 min test
Serial Protocols	Modbus RTU, Modbus ASCII, Laurel ASCII
Modbus Compliance	Modbus over Serial Line Specification V1.0 (2002)
Ethernet Connector	RJ45 jack for 10/100 Base-T Ethernet cable
RS232/485 Connector	Screw terminals for easy daisy chaining
Digital Addresses	247 for Modbus, 31 for Laurel ASCII
Dual Relay Output (standard)
Relay Type	Two solid state relays, SPST, normally open, Form A
Load Rating	120 mA at 140 Vac or 180 Vdc
Power Input
Standard Power	85-264 Vac or 90-300 Vdc
Low Power Option	10-48 Vdc or 12-32 Vac
Power Frequency	DC or 47-63 Hz
Power Isolation	250V rms working, 2.3 kV rms per 1 min test
Power Consumption	2W typical, 3W with max excitation output
Mechanical
Dimensions	129 x 104 x 22.5 mm case
Mounting	35 mm rail per DIN EN 50022
Electrical Connections	Plug-in screw-clamp connectors
Environmental
Operating Temperature	0°C to 55°C
Storage Temperature	-40°C to 85°C
Relative Humidity	95% at 40°C, non-condensing
Cooling Required	Mount transmitters with ventilation holes at top and bottom. Leave 6 mm (1/4") between transmitters, or force air with a fan.

Pinout

Resistance Measurement 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.

Applications

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.

Datasheet, Manual, Mechanical and Serial I/O info.
Manufacturer site:	https://www.laurels.com/transmitter-ohms.php