LT DIN Rail Digital Transmitter with Serial Data Communication and Analog Outputs for Analog Input Totalizer Applications P/N LT61VF3

Analog Input Totalizer Transmitter Frequently Asked Questions

Why does the transmitter convert the analog input to a frequency internally instead of measuring it directly?

Converting to frequency lets the transmitter use the same precise, quartz-referenced period-timing technique used across the LT Series for high accuracy, and makes totalizing straightforward since a frequency signal's pulse count over time directly represents an accumulated quantity.

Why is square root extraction needed for differential pressure flow signals specifically?

Differential pressure flow transducers (used with venturi meters and orifice plates) produce a signal proportional to the square of the actual flow rate due to the physics of pressure drop across a flow restriction; square root extraction reverses that relationship so the displayed rate and total reflect true flow rather than the transducer's raw squared output.

No — accuracy is specified as ±0.01% of full scale ±1 count across all three input types; the choice is determined by which signal type the connected transducer or process loop actually produces, not by any accuracy tradeoff between the three.

What does the 1/rate function actually compute?

It inverts a rate reading into a time value — for example, if a rate signal represents conveyor speed, 1/rate can be scaled to show the time it takes material to travel a fixed distance, such as passing through an oven, rather than showing the speed itself.

Why does gate time selection range from 10 ms up to 200 seconds?

Shorter gate times give faster updates (up to 25 per second) but are best suited to higher-frequency converted signals, while longer gate times average over a longer period, trading update speed for stability — the appropriate gate time depends on how fast the process itself changes and how much update speed the application actually needs.

Can this transmitter totalize a signal that requires custom curve linearization instead of square root extraction?

Yes, with the Extended main board — custom curve linearization uses up to 180 user-entered data points and a spline-fit approach to correct nonlinear transducer outputs that don't follow a simple square-root relationship, extending the totalizer to transducer types beyond standard DP flow.

Does the total remain accurate regardless of which gate time is selected?

Yes — totals are calculated as the product of rate and elapsed time in seconds regardless of the selected gate time, so changing the gate time affects display update speed and averaging but doesn't introduce a systematic error into the accumulated total.

What happens to the total if power is lost mid-process?

Totals are stored in non-volatile memory, so an accumulated total survives a power interruption and resumes from where it left off once power is restored, rather than resetting to zero.

Can this transmitter be used to retrofit totalizing onto an existing 4-20 mA loop without touching the upstream transducer?

Yes — the transmitter simply reads the existing 4-20 mA (or 0-1 mA / 0-10V) signal already present in the loop and adds rate and total tracking on top of it, without requiring any changes to the transducer or upstream wiring generating that signal.

Can multiple analog input totalizer 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.

Analog Input Totalizer Transmitter Questions From the Field

My totalized flow reading seems too low at low flow rates but accurate at high flow — what's the likely cause?

If square root extraction isn't enabled (or is enabled when it shouldn't be) for a differential pressure transducer, low-flow readings will be disproportionately affected because the squared relationship compresses low-end signal more than high-end signal; confirming square root extraction is correctly enabled and matched to the actual transducer type is the standard first check.

My total doesn't match what I'd expect from manually multiplying an average rate by elapsed time — why?

The transmitter calculates total continuously as rate times elapsed time at whatever gate time is set, which accounts for rate variation throughout the period; a rough manual calculation using a single average rate will diverge from this if the actual rate fluctuated meaningfully during that time, rather than indicating a transmitter error.

My reading is unstable specifically at very short gate times — what should I check?

Very short gate times trade averaging stability for speed, so genuine signal noise that would otherwise be smoothed out becomes more visible in the reading; trying a longer gate time is the standard first step to confirm whether the instability is inherent to the signal or specific to the short gate time setting.

My 4-20 mA totalizer reads zero total even though the current loop shows a valid signal — what's the first thing to check?

Confirming the transmitter is actually configured for totalizing mode (rather than rate-only display) and that any external reset input isn't stuck in a reset-active state are the first checks, since a valid input signal with an active reset condition or wrong mode configuration would produce a persistent zero total.

Can noise on the analog input loop cause false total accumulation?

Yes — noise superimposed on the analog signal gets converted along with the genuine signal into the internal frequency, so persistent electrical noise can accumulate into the total over time; checking cable shielding, grounding, and loop wiring quality is the standard remedy for unexpectedly high totals with no corresponding real flow.

My batch fill operation doesn't stop at the expected total — what should I check?

Verifying the preset total configured in setup software matches the intended batch target, and that the relay is actually wired to the correct output configured to trigger at that total, are the standard first steps before suspecting a measurement fault.

Why would switching input type (say, from 4-20 mA to 0-10V) require recalibration?

Each input type uses a different internal input impedance and signal path, so a calibration performed under one input type configuration doesn't automatically carry over to a different input type; recalibrating after changing which analog input type is selected is the recommended practice.