LT DIN Rail Analog Transmitter with Serial Data Communication and Analog Outputs for Process and Ratiometric Signal Applications

Process and Ratiometric Signal Transmitter Frequently Asked Questions

What's the difference between absolute mode and ratiometric mode on this transmitter?

Absolute mode measures the input signal against a fixed internal reference, with accuracy specified as 0.01% of full scale ±2 counts. Ratiometric mode instead measures the signal relative to the transmitter's own excitation voltage, so it automatically compensates for changes in that excitation, with accuracy specified as 0.01% of reading ±2 counts.

What is potentiometer follower mode, and when is it used?

In this mode, the transmitter tracks a potentiometer's wiper position as a ratio of the applied 5V excitation, so the reading follows the mechanical position of the potentiometer rather than an absolute voltage — useful for position feedback applications where excitation stability would otherwise be a concern.

Why do the two most sensitive voltage ranges get 1 GΩ input impedance?

The 200.00 mV and 2.0000V ranges specifically carry 1 GΩ input impedance to minimize the load on the voltage signal, since low-level sources are typically higher-impedance and more easily loaded down by a measuring instrument's own input resistance.

Can this transmitter be used with both bridge circuits and potentiometers in ratiometric mode?

Yes — ratiometric operation uses the transmitter's 5V or 10V excitation output for load cells and Wheatstone bridges, and its 5V excitation output for potentiometers tracking wiper position, covering both sensor types from the same hardware.

What does custom curve linearization let me do that standard scaling doesn't?

Standard scaling maps a signal linearly between two points, but many physical relationships (like liquid volume in an irregularly shaped tank) aren't linear. Custom curve linearization uses up to 180 user-entered data points to build non-linear spline-fit segments, providing much better accuracy than a linear approximation for these applications.

Besides tank volume, what else is custom curve linearization used for?

Altimeters and thermistors are noted as additional applications, since both involve a non-linear relationship between the raw sensor signal and the desired reading that benefits from multi-segment spline fitting rather than a single linear scale.

Why does the 5A current range have a different accuracy spec than the other current ranges?

The 5A range is specified at ±10 mA rather than the 0.01% FS ±2 counts accuracy of the other current ranges, reflecting the practical tradeoff of extending measurement to a higher current level through shunt-based sensing.

Does changing the analog output range require rewiring the output terminals?

No — the output type (4-20 mA, 0-20 mA, 0-10V, or -10 to +10V) is jumper and software selectable on the same terminals, so switching between output types is a configuration change rather than a rewiring job.

What's the difference between the P and SG signal input options for this transmitter?

Both use the same DC signal conditioner board, precalibrated in EEPROM for all standard DC voltage and current ranges; the P and SG designations differ in their default field scaling (4-20 mA in/out vs. 0-200 mV to 0-100.00), with custom scaling available on either as an option.

Can I network multiple process transmitters 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.

Process and Ratiometric Signal Transmitter Questions From the Field

My ratiometric reading changes slightly when the excitation supply voltage fluctuates — is that expected?

Some residual sensitivity can remain even in ratiometric mode if the compensation isn't perfectly matched to the specific sensor's characteristics; if the fluctuation exceeds the specified reading accuracy, checking the excitation wiring connections and verifying the transmitter is genuinely configured for ratiometric rather than absolute mode is the first troubleshooting step.

My tank volume reading is accurate at the top and bottom of the range but off in the middle — what does that suggest?

This pattern points to an inadequate or missing custom curve linearization rather than a sensor fault — a simple two-point linear scale will match at the endpoints by definition but diverge across a non-linear tank shape in between; adding more data points to the custom curve setup typically resolves it.

Why does my potentiometer-based position reading drift or jump at certain positions?

Mechanical wear or dirty contact points on the potentiometer wiper are common causes of erratic readings at specific positions, since the transmitter is faithfully reporting whatever ratio the wiper actually produces; inspecting the potentiometer itself is the standard first step before suspecting the transmitter.

My process signal reads correctly at low input values but clips or maxes out early — what should I check?

This typically points to a scaling or range mismatch between the actual input signal range and what's configured in the transmitter's setup software, rather than a hardware fault; verifying the jumper-selected range matches the sensor's actual output span is the first step.

Can two seemingly identical process transmitters read slightly differently for the same input?

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 tolerance, verifying both units against a known reference signal is the standard field step.

My RS485 network has one process transmitter that intermittently drops off — where should I start?

Confirming that transmitter's address is unique and hasn't drifted from its configured value is a common first step, since an address conflict is one of the most frequent causes of a single unit going silent while the rest of a daisy-chained network continues functioning.

Why would my reading be noisy specifically in a location near variable-frequency drives?

Variable-frequency drives are a well-documented source of electrical noise that couples into nearby signal wiring; checking cable shielding, grounding, and physical separation from the noise source is the standard remedy before suspecting a transmitter fault.