LTE DIN Rail Analog Transmitter with Ethernet Communication and Analog outputs for True RMS AC Voltage and Current Applications

LTE True RMS AC Voltage and Current Transmitter Frequently Asked Questions

Why does True RMS measurement matter compared to average-responding measurement?

Average-responding meters are typically calibrated assuming a pure sine wave and can read significantly wrong on distorted or non-sinusoidal waveforms. True RMS measurement calculates the actual effective value of the waveform regardless of its shape, giving an accurate reading on distorted signals that an average-responding instrument would misrepresent.

What is crest factor, and why does it matter for this transmitter?

Crest factor is the ratio of a waveform's peak value to its RMS value. This transmitter is rated for a crest factor of 3.0 at full scale, increasing to 300 at 1% of full scale, meaning it can accurately measure signals with significant peaks relative to their RMS value — important for distorted waveforms like chopped or rectified AC.

What's the difference between AC coupling and DC coupling on this transmitter?

AC coupling blocks the DC component of a signal, making it suited to applications like measuring ripple on a DC power supply. DC coupling passes the full signal, including any DC offset. Both are jumper selectable, and the transmitter accepts frequencies from DC to 5 kHz depending on coupling and range.

Why does the 5A current range use a built-in shunt instead of requiring a step-down transformer?

The 5A range uses a built-in 0.01 ohm shunt sized specifically to accept the standard output of 5A current transformers directly, eliminating the need for an external step-down transformer between the CT and the transmitter.

Can this transmitter be used safely with a current shunt on the high side of the line?

Yes — high common mode rejection allows for stable readings even with current shunts located on the high side of the line, which is a common requirement in AC current monitoring installations.

How fast does this transmitter produce a reading after a signal changes?

True RMS readings are available 0-16.7 ms after completion of one input signal cycle, allowing anomalies to be detected and alarmed quickly, before they escalate into more costly problems.

Does the Ethernet interface affect measurement accuracy or update rate?

No — accuracy (0.03% FS) and response time come from the same signal conditioning used across the AC RMS product line; Ethernet only changes how the reading is transmitted digitally rather than over serial data.

Is there a version of this transmitter with higher input impedance?

A 10 Megohm input resistance version is available as a factory special, though it reduces the maximum frequency from 5 kHz to 1 kHz for three of the voltage ranges compared to the standard 1 Megohm version.

Does this transmitter include an excitation output like the DC and load cell variants?

No — most LTE models include an isolated transducer excitation output, but AC RMS signal conditioners are a noted exception, since excitation isn't relevant to true RMS AC voltage or current measurement.

Can multiple AC RMS transmitters be networked together?

Yes — the transmitter supports up to 247 digital addresses via Modbus TCP, allowing many individually addressable transmitters to coexist on the same Ethernet network.

LTE True RMS AC Voltage and Current Transmitter Questions From the Field

My AC reading looks different from what another meter on the same circuit shows — which one is right?

If the other meter is an average-responding instrument rather than a True RMS meter, a difference is expected on any non-sinusoidal or distorted waveform, since average-responding meters are typically calibrated for a pure sine wave and will read incorrectly on distorted signals; a True RMS reading is the more accurate one in that case.

My current reading from a CT seems consistently off by a scaling factor — what should I check?

This is commonly a CT ratio scaling issue rather than a transmitter fault — verifying that the transmitter's scaling matches the actual current transformer's turns ratio is the standard first step, since the transmitter reads the CT's secondary output directly and relies on correct ratio scaling to display the primary value.

My reading is unstable on a load with a lot of harmonic distortion — is that a transmitter problem?

Not necessarily — highly distorted waveforms are exactly the case True RMS measurement is designed to handle accurately, but very high crest factor signals beyond the transmitter's rated 3.0 at full scale can push measurement accuracy outside spec; checking the actual crest factor of the signal against the transmitter's rating is a useful diagnostic step.

Why does my reading change when I switch from AC coupling to DC coupling?

AC coupling removes any DC component from the measurement, while DC coupling includes it; if the monitored signal has a genuine DC offset (such as ripple riding on a DC supply), the two coupling modes will legitimately produce different readings by design, not due to a fault.

My transmitter isn't showing up on the network — what should I check first?

Confirming the transmitter's IP configuration matches what the network expects, and that the physical Ethernet cable and switch port are functioning, are the standard first checks before suspecting a transmitter fault.

My transmitter reads correctly at low signal levels but seems to lose accuracy near the top of the range — what's going on?

This is worth checking against the specified accuracy range for the selected input range, since some ranges are specified with a minimum signal level for rated accuracy; confirming the selected range matches the actual signal level (rather than using an oversized range for a small signal) typically resolves apparent accuracy issues.

Can noise from a nearby VFD or motor affect this transmitter's readings?

Yes — like other precision instrumentation, this transmitter's signal wiring is susceptible to noise from variable-frequency drives and motors; checking cable shielding, grounding, and physical separation from the noise source is the standard remedy before suspecting the transmitter itself.

My Modbus TCP polling occasionally times out even though the transmitter appears connected — what's the likely cause?

Network congestion or too many devices polling the same transmitter simultaneously can cause intermittent timeouts; checking polling frequency from all connected clients and network traffic load is a common troubleshooting step.