LTE DIN Rail Analog Transmitters with Ethernet Communication and Analog outputs for Resistance in Ohms

LTE Resistance Transmitter Frequently Asked Questions

Why does excitation current drop from 5 mA on the lowest ranges (R0/R1) down to 80 nA on the highest range (R7)?

Documented specification lists a specific fixed excitation current for each range, decreasing as the range increases — since higher resistance values would produce excessive voltage drop (and potentially damage the device under test or exceed input limits) if driven with the same higher excitation current used on low-resistance ranges, documented practice of scaling excitation current down as resistance range increases is consistent with keeping the developed voltage within the transmitter's measurable and safe input range across all eight documented ranges.

Why does the transmitter's documented "ratiometric mode" matter specifically for resistance measurement, given resistance transmitters use a fixed, known excitation current?

Documented description specifically states the applied excitation current is itself sensed by the meter and automatically compensated for any changes — this indicates that even though each range has a documented nominal excitation current value, the transmitter doesn't simply assume that value stays perfectly constant; by actively sensing the real excitation current and calculating resistance ratiometrically against it, minor drift in the actual excitation current is documented as not translating into a proportional measurement error.

Does the QA passband mode's documented 50 mΩ example represent a fixed, built-in deviation limit, or a configurable example value?

Documented description specifically presents 50 mΩ as "this example," language indicating it's an illustrative figure rather than a fixed, hardcoded limit — the underlying passband mode is documented as setting a deviation limit "around both sides of a setpoint," which is consistent with the specific deviation width being a user-configurable parameter for a given production testing application rather than a single universal fixed value.

Why are R0, R6, and R7 documented as "factory-set fixed" ranges while R1 through R5 are documented as jumper-selectable?

The page documents this distinction (R0/R6/R7 as factory-fixed, R1-R5 as jumper-selectable and precalibrated) without detailing the underlying circuit design reason — this is consistent with the three factory-fixed ranges representing the extremes of the transmitter's measurable span (the most sensitive 2Ω range and the two highest-resistance Mohm ranges), which may require dedicated, non-reconfigurable circuit elements, while the five jumper-selectable ranges in between share circuitry that supports field reconfiguration via jumper.

Does the documented note that "the same signal conditioner board can be used for resistance and RTD temperature measurement" mean an RTD transmitter and a resistance transmitter are functionally identical hardware?

Documented note specifically states the same board can be used for both, which is consistent with a shared underlying hardware platform — however, this page and the separate RTD temperature transmitter page document different, purpose-specific software/firmware configurations built on that shared board (temperature linearization and per-type conformity handling for RTD mode, versus direct resistance readout for this mode), so the two represent different documented configurations of common hardware rather than functionally identical products.

Does this LTE Resistance transmitter's documented Modbus TCP-only protocol limit compatibility compared to the RS232/RS485 LT Series resistance variant?

Yes — this page documents Modbus TCP specifically as the supported Ethernet Data I/O protocol at digital address 247, while the LT Series serial variant is documented elsewhere as separately supporting Modbus RTU/ASCII and Laurel Custom ASCII; a control system needing a protocol other than Modbus TCP would need to reference the LT Series serial variant rather than this LTE Ethernet variant.

Does selecting the Extended main board for custom curve linearization change this transmitter's documented resistance measurement accuracy?

No — documented Extended board capability (custom curve linearization, rate from consecutive readings) is described as an additive processing feature layered on top of the underlying measurement; the documented ±0.01% of reading ±2 counts accuracy figure applies to the underlying resistance signal conditioning regardless of whether the Standard or Extended main board is selected.

Does the 0.1 milliohm resolution documented specifically for the 2 ohm (R0) range apply proportionally to the other seven ranges as well?

No — documented resolution figures are listed individually per range (0.1 mΩ on R0, scaling up to 1000 Ω on R7), each tied to that specific range's own full-scale span and the shared 16-bit (65,536-step) input resolution; the specific milliohm-level resolution highlighted for contact resistance testing is documented as a characteristic of the R0 range specifically, not a resolution figure that carries over unchanged to the higher-resistance ranges.

Can the same physical transmitter be reconfigured in the field between different jumper-selectable resistance ranges (R1-R5), or does each require separate hardware?

Documented specification lists R1 through R5 specifically as "jumper-selectable, precalibrated" ranges, distinct from the factory-fixed R0/R6/R7 ranges — this is consistent with a single physical unit supporting field reconfiguration across these five ranges via jumper setting, since each is documented as already precalibrated at the factory rather than requiring a separate signal conditioner board purchase for each range.

Does the transmitter's documented ±0.01% of reading accuracy specification apply identically whether operating in 2-wire, 3-wire, or 4-wire hookup mode?

The page documents this accuracy figure once, under the general Signal Input specification, without listing separate accuracy figures specifically for each of the three wiring configurations — however, since 2-wire hookup is documented as not compensating for lead resistance changes due to ambient temperature (unlike 3- and 4-wire), the wiring configuration selected can affect real-world accuracy in installations with meaningful lead length or temperature variation, even though the transmitter's own core specification is expressed as one figure.

4-Wire Kelvin Contact Resistance Testing Questions From the Field

What specifically is the 4-wire Kelvin method, and why is it specifically suited to measuring very low resistances like contact joints?

Documented explanation specifically describes the Kelvin method as isolating current injection from voltage sensing using two separate lead pairs — one pair carries a known test current, while a separate pair senses the resulting voltage drop; documented analysis specifically notes that for resistances under 1Ω, lead and contact resistance in a standard 2-wire measurement can account for a large percentage of the total reading, rendering that data essentially useless, which is precisely the error the Kelvin method's separated current/sense paths are documented as eliminating.

Is there a documented typical test current range recommended for measuring contact resistance around 10 mΩ specifically?

Yes — documented guidance specifically recommends a test current in the 50-200 mA range for targeting approximately 10 mΩ contact resistance measurements, chosen specifically to yield a measurable voltage drop without causing significant self-heating of the joint being tested; this documented figure sits within a broader general recommended range of 10 mA to 1 A depending on the specific resistance target.

Does clamping force or probe pressure genuinely affect contact resistance test repeatability, or is this a minor factor?

It's documented as a genuine, quantified factor — documented best practice specifically recommends maintaining repeatable clamping force using torque drivers or spring probes held within ±5% consistency, directly tying probe contact force to measurement repeatability rather than treating pressure as a negligible variable in the test setup.

Does current reversal during a contact resistance test serve a genuine documented measurement-accuracy purpose, or is it purely a convention?

It serves a genuine documented purpose — documented guidance specifically recommends using current reversal specifically to cancel out offset errors introduced by thermal EMF (small voltages generated at junctions of dissimilar metals due to temperature differences); documented practice specifically recommends averaging at least four reversals to obtain a reading free of this thermal EMF-driven offset.

Is contamination or oxidation on the contact surface being tested a documented significant source of measurement error, separate from the test equipment itself?

Yes — documented best practice specifically recommends cleaning contacts with 99% isopropyl alcohol and removing oxides with a gentle abrasive or appropriate chemical treatment before testing, since surface contamination and oxidation are documented as directly adding to measured contact resistance independent of any error contributed by the test instrument or probes themselves.

Does worn or degraded test probe hardware itself introduce a documented, measurable error into contact resistance readings over time?

Yes — documented guidance specifically states that worn probes can shift readings by several microohms and should be replaced, explicitly identifying probe wear as its own distinct, quantified error source separate from the actual joint or contact being measured, which is why documented practice includes probe condition as an ongoing maintenance check.

Is periodic verification against a traceable reference standard documented as necessary before running a contact resistance test campaign, or is factory calibration alone considered sufficient?

Documented best practice specifically recommends validating the measurement setup against traceable reference standards (such as 1 mΩ and 10 mΩ references) before beginning a measurement campaign, in addition to confirming the instrument's own calibration is current within the last 12 months; this documented two-part verification (instrument calibration plus setup validation against known references) is presented as standard practice rather than relying on factory calibration alone.

Is a simpler 2-wire resistance check ever documented as an acceptable substitute for full 4-wire Kelvin testing in a production or field environment?

Yes, in a specific limited context — documented field guidance specifically notes that 2-wire measurement is commonly used to monitor degradation trends over time rather than to establish an exact baseline value, with a practical strategy documented as combining periodic 2-wire checks with occasional 4-wire calibration runs; this is presented as a genuine, documented tradeoff between measurement convenience and absolute accuracy, not a recommendation to abandon 4-wire testing altogether for critical baseline measurements.