Features
- Five jumper-selectable resistance ranges of 20.000 ohm to 200.00 kohm
- Three fixed factory-special resistance ranges of 2.0000 ohm, 2.0000 Mohm, 20.000 Mohm
- Accuracy at 25°C ±0.01% of reading ± 2 counts
- 0.1 milliohm resolution on 2 ohm scale for contact resistance measurements
- 2, 3 or 4-wire connection with lead resistance compensation
- All input ranges are user selectable and factory calibrated
- Up to 60 conversions per second, Ideal for peak or valley capture
- 4-20 mA, 0-20 mA, 0-10V or -10V to +10V transmitter output, (isolated)
- Analog output resolution 0.0015% of span, accuracy ±0.02% of span
- RS232 or RS485 serial data, Modbus or Laurel ASCII protocol (isolated)
- Dual 120 mA solid state relays for alarm or control (isolated)
- Power 85-264 Vac / 90-300 Vdc or 10-48 Vdc / 12-32 Vac (isolated)
- DIN rail mount housing, 22.5 mm wide, detachable screw-clamp connectors
- Operating temperature from -40°C to 70°C (-40°F to 158°F)
Optional - Extended allows up to 180 data points for custom curve linearization and a rate derived from consecutive readings.
Certificates of Compliance
The Laureate 4-20 mA, 0-20 mA, 0-10V or -10V to +10V and RS232/RS485 output transmitter for resistance in ohms offers the same high performance, signal conditioning and programmable features as Laureate digital panel meters, counters & timers provides six voltage input ranges and four current input ranges, all factory calibrated and jumper selectable. The Resistance in Ohm 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, 2.0000 Mohm and 20.000 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 signal conditioner board ranges are factory-calibrated, with calibration factors for each range securely stored in an onboard EEPROM. These factors can be scaled via software to accommodate external shunts, enabling field replacement of signal conditioner boards without necessitating recalibration of the associated transmitter. For optimal accuracy, factory recalibration is recommended annually. All Laurel Electronics instruments undergo factory calibration using the industry-leading Fluke calibrators, which are recalibrated yearly and certified traceable to national standards, ensuring the highest level of precision and reliability.
The optional extended Laureate computer board enhances Laureate transmitter by displaying rates derived from successive readings and enabling highly accurate custom curve linearization. For example, it can calculate liquid volume or flow rate in a horizontal cylindrical tank using levels from a 4-20 mA transmitter. Setup is straightforward: users input up to 180 data points into a spreadsheet or text file, and the computer calculates spline-fit segments, which are then downloaded to the transmitter for precise operation.
Laureate Transmitters are easily programmed with Laurel’s free Instrument Setup Software, downloadable from our website and compatible with Windows PCs, requiring a data interface board for setup.
High read rate of up to 50 or 60 conversions per second, the Laureate™ LT Series transmitter uses Concurrent Slope (US Pat. 5,262,780) analog-to-digital conversion to integrate signals over a full power line cycle (50 Hz or 60 Hz). This read rate enables peak and valley capture, real-time computer interfacing, and control applications. Peak and valley values are automatically captured and can be viewed using Laurel’s free Instrument Setup Software (compatible with Windows PCs) or transmitted as serial data.
Standard Hardware Features of Laureate LT Transmitters Include:
- Serial communications output, (isolated), 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.
- 4-20 mA, 0-10V or -10V to +10V analog transmitter output, (isolated), jumper-selectable and user scalable. All selections provide 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. Note that Ethernet data I/O is provided by Laurel's LTE series transmitters.
- Dual solid state relays, (isolated), for alarm or control. Rated 120 mA at 130 Vac or 180 Vdc.
- Selectable transducer excitation output, (isolated), user selectable 5V@100 mA, 10V@120 mA, 12V@100mA, or 24V@50 mA.
- Power 85-264 Vac, (isolated), low-voltage 10-48 Vdc or 12-32 Vac power is optional.
Digital signal filtering modes can be selected to ensure 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.
- An adaptive moving average filter selection provides a choice of 8 time constants from 80 ms to 9.6 seconds. 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.
Two tare functions: auto-tare and manual tare. In auto-tare, an input line is grounded by an external pushbutton. This causes the current weight, which is normally the empty weight of the container to be stored in memory as an offset. In manual tare, the tare value can be entered manually via a control input pushbutton or using Laurel's free Instrument Setup Software.
Peak and valley values are automatically captured. These may be displayed via Laurel's free Instrument Setup Software, which runs on a PC under MS Windows or can be transmitted as serial data.
Two control inputs (CMOS/TTL levels, logic 0 = tied to digital ground, logic 1 = open) or dry contacts that can be set to control / activate 14 transmitter commands.
LT series DIN rail Transmitters & signal conditioners can be interfaced to a wide range of sensors and transducers using one of seven available plug-in signal conditioner boards. The transmitters duplicate the high performance (high accuracy, high read rate) and extensive programmable features of Laureate 1/8 DIN digital panel meters, counters and timers. They utilize the same signal conditioners boards, much of the same firmware, and Laurel's free Windows-based Instrument Setup Software. They come in a compact DIN rail mount package with detachable screw-clamp connectors for easy wiring.
The LT series Transmitters feature isolated, user-selectable analog outputs (4-20 mA, 0-20 mA, 0-10V, or -10V to +10V), an RS232 or RS485 serial data interface, and dual 120 mA solid state AC/DC relays. Most models, except those with temperature or AC RMS signal conditioners, include an isolated 5, 10, 12, or 24 Vdc transducer excitation output.
Connecting Laureate LT Transmitters to a Local Area Network (LAN)
Up to 30 Laureate LT Transmitters and/or Digital Panel Meters can be configured for RS485 and daisy-chained to an LT Transmitter for seamless LAN integration. Alternatively, Laurel LTE series Ethernet transmitters can connect directly to a LAN via an Ethernet cable. Setup for both configurations is streamlined using Laurel’s free Instrument Setup Software, which simplifies node discovery and transmitter configuration.
Flexible Communication Options for LT Transmitters
Laureate Transmitters can be equipped with Laurel communication boards to support various interfaces and protocols. These include serial interfaces with ASCII or Modbus RTU protocols, and Ethernet interfaces with web access, ASCII, or Modbus TCP/IP protocols, ensuring versatile connectivity for your commercial applications.
| LT Transmitter Signal Input & Function | Model Series | Analog Output | RS232 & RS485 | Dual Relays | |
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| 1 | DC Input Voltage and Current | LT-DC |  |
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| 2 | AC RMS Voltage or Current | LT-RMS | |
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| 3 | Process Voltage or Current | LT-P | |
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| 4 | Weighing Applications | LT-WA | |
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| 5 | Load Cell & Microvolt Signals | LT-WM | |
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| 6 | Thermocouple (Types J, K, T, E, N, R, S) | LT-TC | |
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| 7 | RTD Temperature | LT-RTD | |
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| 8 | Resistance in Ohms | LT-R | |
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| 9 | Frequency, Rate, Speed | LT-FR | |
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| 10 | Pulse Input Totalizer | LT-FR | |
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| 11 | Process Signal Totalizer | LT-VF | |
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| 12 | Sum, Difference, Ratio, Product of 2 Inputs | LT-FR | |
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| 13 | Batch Controller Pulse Input | LT-FR | |
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| 14 | Batch Controller Analog Input | LT-FR | |
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| 15 | On/Off Duty Cycle | LT-FR | |
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| 16 | Stopwatch Timing for Single Events | LT-FR | |
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| 17 | Average Time of Periodic Events | LT-FR | |
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| 18 | AC Phase Angle and Power Factor | LT-FR | |
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| 19 | Quadrature Position or Rate | LT-QD | |
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Ethernet & 4-20 mA Output Thermocouple Temperature Transmitter
| Range | Ohms | Resolution | Accuracy | Excitation Current *** |
|---|---|---|---|---|
| R0** | 0-2.0000 Ω | 0.1 mΩ | ±0.01% of reading ± 2 counts |
5 mA |
| R1* | 0-20.000 Ω | 1 mΩ | 5 mA | |
| R2* | 0-200.00 Ω | 10 mΩ | 500 µA | |
| R3* | 0-2000.0 Ω | 100 mΩ | 50 µA | |
| R4* | 0-20000 Ω | 1 Ω | 5 µA | |
| R5* | 0-200.00 kΩ | 10 Ω | 500 nA | |
| R6** | 0-2.0000 MΩ | 100 Ω | 500 nA | |
| R7** | 0-20.0000 MΩ | 1000 Ω | 80 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. | ||||
| Recalibration: All ranges are calibrated at the factory. Recalibration is recommended every 12 months. | ||||
| 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, Custom ASCII | |||
| Modbus Compliance | Modbus over Serial Line Specification V1.0 (2002) | |||
| RS232/485 Connector | Screw terminals for easy daisy chaining | |||
| Digital Addresses | 247 for Modbus, 31 for Custom 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 at 24V | 1.5W typical | |||
| Environmental | ||||
| Operating Temperature | -40°C to 70°C (-40°F to 158°F) | |||
| Storage Temperature | -40°C to 85°C (-40°F to 185°F) | |||
| 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. | |||
| Mechanical | ||||
| Enclosure | Rugged black polycarbonate housing material | |||
| Mounting | 35 mm rail per DIN EN 50022 | |||
| Dimensions | 129 x 104 x 22.5 mm case | |||
| Connectors | Detachable screw clamp connectors meet VDE / IEC / UL / CSA standards. RJ45 jack for Ethernet | |||
| Tightening Torque | Screw terminal connectors: 5 lb-in (0.56 Nm) | |||
| Weight | Complete transmitter: 183 g (6.5 oz) | |||
| Replacement Case Screws | ||||
| Size | 6 | |||
| Thread Pitch | 6-19 | |||
| Length | 1/2" | |||
| Head Style | Pan Head | |||
| Drive Style | Phillips | |||
| Head Diameter | 0.256-0.270 | |||
| Head Height | 0.087-0.097 | |||
| Full/Partial Thread | Full | |||
| Drive Size | 2 | |||
| Material | Steel | |||
| Finished | Black Oxide | |||
| General | ||||
| Programming | Utilize Laurel's free Instrument Setup Software, which runs on a PC under MS Windows. | |||
| Security | Lockout options available using Laurel's free Instrument Setup Software. | |||
| Warranty | 3 years parts & labor | Recalibration: All ranges are calibrated at the factory. Recalibration is recommended every 12 months. | ||
Transmitter 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. | |
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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. |
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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. |
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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. |
Free Instrument Setup Software for Series 2 Laureates
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| 1/8 DIN Digital Panel Meters | DIN Rail Transmitters |
Free Downloadable Windows-based Instrument Setup (IS) software (Data Interface Board Required) for use with our programmable Digital Panel Meters, Scale Meters, Counters, Timers, Remote Displays, and Transmitters, are an easy method to set up Laureate 1/8 DIN digital panel meters, counters, timers, remote displays, and DIN-rail transmitters, as explained in the Instrument Setup Software Manual. Laureate 1/8 DIN instruments can also be set up from the front panel, as explained in their respective Owners Manuals. Instrument Setup software is of benefit whether or not the PC is connected to the instrument.
- When the PC is connected to the instrument, Instrument Setup software can retrieve the setup file from the instrument or open a default setup file or previously saved setup file from disk View Setup, then provides graphical user interface (GUI) screens with pull-down menus applicable to input, display, scaling, filtering, alarms, communications, analog output, and front panel lockouts. Fields that are not applicable to the instrument as configured are either left out or grayed out. Clicking on any item will bring up a detailed Help screen for that item. After editing, the setup file can be downloaded, uploaded to the instrument, or saved to a disk. The same setup file can then be downloaded into multiple instruments.
- When the PC is not connected to the instrument, the above GUI screens can be used to set up a virtual instrument. The setup file can then be saved to disk. Switching toView Menu then brings up a screen with the required front panel programming steps. This view can be printed out for use at the instrument site and to serve as a hard copy record.
Download Free Instrument Setup Software
Installation
Set User Account Control (UAC) of MS Windows to "Never notifiy me" so that Instrument Setup Software can create directories. The UAC change screen can be reached as follows:
- Under Windows 7, click on the Windows Start button in the lower left of the desktop and enter "UAC" in the search field.
- Under Windows 8, navigate to Control Panel, then to the "User Accounts and Family Safety" section, and click on "Change User Account Control Settings."
- Under Windows 10, click on the Windows Start button in the lower left of the desktop, then on "Settings", and enter "UAC" in the search field.
- Reboot your computer for the changed UAC setting to take effect.
RJ11-to-DB9 cable with rear view of DB9 connector to PC
RS232 cable, meter to PC, P/N CBL01
Laureate 1/8 DIN Laureate instruments must be equipped with a serial communications board and be connected to the computer via a serial communications cable. The connection can be via RS232, RS485, USB or Ethernet. Following setup, the serial communications board may be removed from the instrument if desired. The wiring of the RS232 cable is illustrated above with end views of the two connectors.
Laureate LT Series transmitters come standard with a 3-wire serial interface, which can be jumpered for RS232 or RS485.
Laureate LTE Series transmitters come standard with an Ethernet interface.
Meter Setup Screens
Click on any of the reduced screens below for a full-size screen view, then click on the Back button of your browser to return to this page. The screens examples below are for a fully-loaded Series 2 Digital Panel Meter (DPM), which is connected to the PC via RS232. If the meter is a Series 1 meter (pre-2007), this is sensed by the software, and somewhat different screens are brought up. Please see Series 1 setup screens.
Welcome Screen
From the computer desktop, click on Start > Programs > IS2 > IS2. Or click on the IS icon on your desktop. This splash screen will be displayed for three seconds. The software revision number is in the lower right.
Communications Selection Screen
Specify your desired communication protocol and the serial communications bus type, which should match the jumper setup of the instrument. Select None if the PC is not connected to the instrument.
Establish Communications Screen
If you selected RS-232, you will be asked to specify the PC Com Port and Baud Rate, which should match the jumper setup of the instrument. Click on Establish. With the right settings, the Communications Established field will light up in green, and the Meter Type will be recognized. If so, click onMain Menu.
Main Menu Screen
Click on File > Default Setup to retrieve the default setup file from disk for your type of meter. Click on File > Open Setupto retrieve a previously saved setup file from disk or on File > Save Setup to save your edited setup file to disk. Click onDPM > Get Setup to retrieve the setup file from your meter or on DPM > Put Setup to download your edited setup file into the meter.
DPM Input + Display Setup Screen
From the Main Menu, click on View > Setup, then on theInput+Display tab. You can now specify the meter hardware, signal type, display mode, and functions of control inputs A and B. Clicking on any item brings up a pull-down menu with the available choices.
DPM Scaling Setup Screen
Click on the Scaling tab, which provides three scaling methods to relate the signal to the displayed reading: 1) Scale and Offset method, 2) Coordinates of two points method, and 3) Reading Coordinates of Two Points method. The last method uses actual high and low signals, and the computer will prompt you.
DPM Filter Setup Screen
Click on the Filter tab, which allows you to specify the digital filter time constant (if any), the adaptive filter threshold, and whether Peak / Valley values are filtered or unfiltered. As for all setup screens, clicking on the F1 key while an item is highlighted brings up a Help screen for that item, as illustrated.
DPM Relay Alarms Setup Screen
Click on the Relay Alarms tab, which allows you to set up Alarms 1 and 2 for the optional dual relay output board. Clicking on any of the four numeric fields changes these to green and brings up a special field to enter the desired numeric value, which is tied to the displayed reading.
DPM Communications Setup Screen
Click on the Communications tab so set up serial communications. In particular, you can special the Serial Protocol and the meter address if multiple meters are to be addressed on the same serial data line.
DPM Analog Output Setup Screen
Click on the Analog Out tab so set up the optional analog output board. Three output ranges are selectable, the endpoints of which can be tied to user-specified High and Low readings.
DPM Lockouts Setup Screen
Click on the Lockouts tab to check off menu items which will no longer be accessible from the front panel of the meter. This will simplify meter operation and prevent unintended setup changes.
Meter Setup Utilities
DPM Front Panel Setup Screen
As an aid to programming the meter from the front panel when a serial connection is not available, you can return to the Main Menu and click on View > Menu. The required sequence of front panel screens will then be displayed. Click on any step in the sequence for the meaning of each digit, as illustrated for the FILtEr step. For a hardcopy, simply press on Print.
DPM Jumper Setup Screen
Specify your desired communication protocol and the serial communications bus type, which should match the jumper setup of the instrument. Select None if the PC is not connected to the instrument.
DPM Jumper Setup Screens
Click on any of the displayed plug-in boards, and you will be presented with the jumper positions and electrical connections for your selected board. This minimizes the need to refer to the printed manual.
DPM Commands Screen
This page allows you set up external input, serial communications, an analog output proportional to the display (optional), and lockouts for Laureate digital counters. The grayed out area at the top right of the screen applies to Laureate remote displays.
Graphical Output Screens (not available with Ethernet)
From the Main Menu, click on Readings if your PC is connected to the meter. A pull-down menu then offers three choices: List, Plot and Graph.
- List presents the latest readings in a 20-row by 10-column table. Press Pause at any time to freeze the display. This is one method to capture peak readings.
- Plot generates a plot of readings vs. time in seconds. It effectively turns the DPM-PC combination into a printing digital oscilloscope.
- Graph generates a histogram where the horizontal axis is the reading and the vertical axis is the number of occurrences of readings. The display continually resizes itself as the number of readings increases.
DPM Calibration Screens
Click on the Scaling tab, which provides three scalClick on the Scaling tab, which provides three scaling methods to relate the signal to the displayed reading: 1) Scale and Offset method, 2) Coordinates of two points method, and 3) Reading Coordinates of Two Points method. The last method uses actual high and low signals, and the computer will prompt you.
Frequency Meter Calibration Screen
Calibration of the quartz crystal of the Laureate frequency meter requires the input of a known frequency from a calibrator. Apply the frequency, then enter the frequency in Hertz. Calibration will be automatic, with storage of the calibration factor stored in non-volatile memory.
Dimensions
Dimensioned CAD assembly drawings in EPRT, STEP, x_t, .dwg, pdf file formats: Laureate-transmitter-case.zip (zipping prevents browser from opening CAD files as text files).
QA Application with Relays in Passband Mode
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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. |
CAL-Analog
Certificate of Calibration
$65.00
CBL02
USB-to-RS232 Adapter Cable
$47.00
CBL04
RS232 Cable for LT Transmitters
$47.00CBL12
12-foot Power Cable
$47.00CBL6
6-foot Power Cable
$41.00What Is the LT DIN Rail Analog Transmitter for Resistance in Ohms?
In industrial and automation settings, precise resistance measurement and monitoring are crucial for ensuring the proper functioning of systems. The LT DIN Rail Analog Transmitter for resistance in ohms is a versatile device engineered to convert resistance measurements into both a standardized analog output and digital serial data, mounted on a DIN rail for straightforward integration into existing control panels.
Industries That Use This Transmitter
- Electronics and Component Manufacturing — high-speed contact resistance testing on production lines using the QA passband relay mode.
- Power Generation and Utilities — insulation resistance measurement on motors, transformers, and switchgear to detect winding degradation before failure.
- Process Industries — reading resistance-based sensors such as RTDs, thermistors, level sensors, and pressure sensors as part of broader process control loops.
- Laboratories and Calibration Facilities — precision resistance verification in test circuits and calibration setups requiring traceable accuracy.
- Industrial Automation — integrating resistance-based feedback into automated control and monitoring systems.
Resistance Ranges and Resolution
Eight resistance ranges are available, from 0-2.0000Ω up to 0-20.000 MΩ. Five of these (20Ω through 200 kΩ) are jumper-selectable and precalibrated; the three widest and narrowest ranges (2Ω, 2 MΩ, and 20 MΩ) are factory-set fixed ranges. Resolution is one part in 20,000 across the board — down to 0.1 milliohm on the 2Ω range, specifically suited to contact resistance measurements where even small resistance changes matter. Each range applies its own fixed excitation current, from 5 mA on the lowest ranges down to 80 nA on the 20 MΩ range, with the transmitter operating ratiometrically so it automatically compensates for any variation in that applied excitation.
2-Wire, 3-Wire, and 4-Wire Lead Compensation
Connections can be made via 2, 3, or 4 wires, with the wiring choice determining how well lead resistance is compensated. In a 4-wire hookup, separate lead pairs carry the excitation current and sense the voltage across the unknown resistance, so lead resistance isn't a factor at all. In a 3-wire hookup, the transmitter measures the combined resistance-plus-lead voltage drop, separately measures one excitation lead's drop, and subtracts twice that value — canceling lead resistance and compensating for ambient temperature changes provided both excitation leads are identical. In a 2-wire hookup, lead resistance is measured once (by shorting the resistance during setup) and subtracted as a fixed offset, which doesn't account for later temperature-driven changes in lead resistance.
QA Passband Mode for Production Testing
For contact resistance testing in a production environment, the relay outputs can be configured in a deviation (passband) mode: a deviation limit is set on both sides of a target setpoint, and the relay closes or opens depending on whether the reading falls inside or outside that band. This makes fast, repeatable pass/fail resistance testing possible without needing external comparator logic.
Conclusion
The LT DIN Rail Analog Transmitter for resistance in ohms gives a panel builder a factory-calibrated way to turn a resistance measurement — from a contact resistance check in the milliohms to an insulation resistance reading in the megohms — into both an isolated analog output and networkable serial data. Its combination of eight selectable ranges, flexible 2/3/4-wire lead compensation, and a built-in QA passband testing mode makes it a fit across production testing, insulation monitoring, process control, and calibration work alike.
Resistance in Ohms Transmitter Frequently Asked Questions
Why does each resistance range use a different excitation current?
Excitation current is scaled inversely to the range so the resulting voltage signal stays in a measurable range without exceeding safe power dissipation in the resistance being measured — a low range like 2Ω uses a relatively high 5 mA excitation, while the 20 MΩ range uses just 80 nA to avoid excessive voltage across a very high resistance.
What's the difference between the jumper-selectable ranges and the "factory-special" fixed ranges?
The five middle ranges (20Ω through 200 kΩ) are jumper-selectable on the same board, so switching between them is a configuration change. The three extreme ranges (2Ω, 2 MΩ, 20 MΩ) are factory-set fixed ranges, meaning a specific unit is built and calibrated for one of those ranges rather than being switchable among them in the field.
Why is 0.1 milliohm resolution on the 2Ω range specifically useful?
Contact resistance measurements — checking connector, switch, or weld joint quality — often deal with resistances in the tens or hundreds of milliohms, where small changes matter. The fine 0.1 mΩ resolution on this range makes it possible to detect meaningful degradation or defects that would be invisible on a coarser scale.
How does QA passband mode differ from a standard high/low alarm setpoint?
A standard setpoint triggers when a reading crosses a single threshold in one direction. Passband mode instead defines a band around a target value and triggers based on whether the reading falls inside or outside that band on either side, which is the natural fit for pass/fail component testing where both too-high and too-low resistance indicate a defect.
Can this transmitter measure insulation resistance in the megohm range?
Yes — the two highest ranges (2 MΩ and 20 MΩ) are specifically suited to insulation resistance measurement on equipment like motor windings and transformers, where healthy insulation reads very high resistance and degradation shows up as a falling reading over time.
When should I use a 3-wire connection instead of 4-wire?
4-wire gives the most complete lead resistance cancellation since excitation and sensing use entirely separate leads. 3-wire is a reasonable middle ground when a 4th wire isn't practical, canceling lead resistance mathematically provided both excitation leads have matched resistance and temperature behavior.
Does the transmitter's ratiometric operation affect how excitation current variation impacts the reading?
No in a good way — ratiometric operation means the transmitter senses the actual applied excitation current and compensates automatically for variations in it, so small changes in the excitation source don't translate into resistance measurement errors.
Can I use the Extended board's custom curve linearization with a resistance input?
Yes — the optional Extended board's custom curve linearization isn't limited to voltage or current inputs; it can be applied to a resistance signal conditioner as well, useful for applications where the resistance-to-physical-quantity relationship isn't linear.
Does this transmitter include an excitation output for other sensor types, like the DC or load cell versions?
The resistance signal conditioner applies its own fixed, range-specific excitation current for the resistance measurement itself, which is a purpose-built current source rather than the general-purpose selectable excitation output (5V/10V/12V/24V) available on non-temperature, non-AC-RMS LT models.
Can multiple resistance transmitters be networked together?
Yes — up to 30 LT Transmitters and/or Digital Panel Meters can be daisy-chained on RS485 for LAN integration, or an LTE series Ethernet transmitter can be used instead for a direct Ethernet connection.
Resistance in Ohms Transmitter Questions From the Field
My contact resistance readings are inconsistent from part to part even though they should be identical — what should I check?
Inconsistent contact readings often trace to probe contact quality (pressure, cleanliness, or oxidation at the test point) rather than a transmitter fault, since contact resistance measurements are especially sensitive to the quality of the probe-to-part connection itself; checking probe condition and contact force is the standard first step.
My insulation resistance reading is dropping gradually over time on equipment that seems to be running fine — what does that mean?
A gradual downward trend in insulation resistance is a well-documented early indicator of insulation degradation in motors and transformers, often preceding an actual fault by a significant margin; tracking the trend over time (rather than a single reading) is the standard practice for catching this kind of gradual failure.
Why would my reading on the 2Ω range be noisy or unstable compared to a higher range?
Low-resistance ranges are more susceptible to the effects of any uncompensated lead or contact resistance, since these are a larger fraction of the total reading at low ohm values; verifying the wiring configuration (2/3/4-wire) matches what's expected for the accuracy needed is the standard first check.
My QA passband relay is rejecting parts that measure within spec on a handheld meter — what should I check?
Confirming that the deviation band and target setpoint are configured to match the actual acceptable tolerance for the part, rather than a default or previously used value, is the first step, since a passband mode set too tight or centered incorrectly will reject otherwise good parts.
Can two transmitters set to the same nominal range read slightly differently for the same resistance?
Small unit-to-unit differences can occur since each unit's factory calibration is specific to its own signal conditioner board; if the difference exceeds the specified 0.01% of reading ± 2 counts tolerance, verifying both units against a known precision resistance standard is the recommended step.
Why does switching from 2-wire to 4-wire change my calibration results on the same part?
Moving to 4-wire sensing removes lead resistance from the measurement entirely, while 2-wire includes a fixed lead resistance offset captured at setup; a calibration performed under one wiring configuration doesn't carry over correctly after changing wiring, so recalibrating after any wiring change is recommended.
My reading is noisy specifically near switching equipment or motor drives — why?
Resistance measurement circuits, especially on the higher-impedance megohm ranges, are susceptible to electrical noise from nearby switching equipment; checking cable shielding, grounding, and physical separation from the noise source is the standard remedy before suspecting the transmitter itself.
