This simulator traces a two-wire loop-powered pressure transmitter through series conductor resistance, a receiver shunt resistor, an analog-to-digital converter and PLC engineering-unit scaling. Adjust the applied pressure, transmitter and PLC span settings, loop supply, wire resistance, receiver shunt and injected transmitter faults to see when the loop stays within its voltage budget and when scaling settings silently disagree.
• A real-time 3D model of the pressure process fixture with its own local gauge, the two-wire transmitter, the loop power supply, outgoing/return cabling with animated current-flow markers, the precision receiver shunt, the analog input converter and the scaled pressure display, with home view, focus-selected-part, toggleable full-enclosure cutaway, exploded view, auto-rotate, expand and show/hide labels controls, and tappable numbered components with callouts. • Seven live controls: applied pressure (0–100 bar), transmitter full scale (25–200 bar), PLC scaling full scale (25–200 bar), loop supply (10–30 V), total conductor resistance (0–1500 Ω), receiver shunt (100–500 Ω), and a transmitter/circuit fault selector (healthy, open loop, low diagnostic current, high diagnostic current). • Play/pause, single-step (0.1 s) and larger-step (1 s) time controls, plus a playback-speed selector (10× slow motion, real time, 10× faster, 1 minute per second). • Start trial and Stop trial actions, with a live sequence narrative and per-component status. • Eight live metrics: transmitter demand, actual loop current, receiver voltage, transmitter terminal voltage, illustrative raw ADC counts (0–27648 scale), PLC engineering value, scaling/signal error, and signal-valid quality flag. • A Curves & measurements tab with two charts (requested vs. actual current, and receiver drop vs. transmitter terminal voltage), the full model equations, and snapshot measurements. • An Experiments tab with four guided scenarios (live zero, full scale, compliance failure, scaling mismatch), a model-verification bench of independent automated checks, and a timestamped event log with a copyable trial report. • A Learn & assess tab with four guided lessons, a two-question knowledge-check quiz, and a written scope/reference statement.
The transmitter requests 4 mA at zero applied pressure and 20 mA at its configured full scale — 4 mA is a healthy "live zero," not a fault, which distinguishes it from an open loop reporting zero current. The loop's available compliance voltage is (Vsupply − 12 V minimum transmitter headroom) divided by the total series resistance of the conductors plus the receiver shunt; when that available current capacity falls below the requested current, actual loop current is limited below the request even though nothing else is broken — this is the "compliance-limited" state distinct from an ordinary healthy signal.
Because the model treats series wire resistance as pure voltage-budget consumption rather than something that changes regulated current on its own, added cable resistance only affects the actual delivered current once it pushes the loop past its compliance limit — a lesson reinforced by the built-in check that identical current results whether wire resistance is 0 Ω or 200 Ω, as long as compliance remains available.
The equations panel gives Irequest = 4 + 16 × clamp(P/transmitterSpan, 0, 1) mA, Imax = max(0, Vsupply − 12 V)/(Rwire + Rshunt), and Pscaled = (I − 4)/16 × PLCspan. Because the PLC's scaling span is set independently from the transmitter's actual span, a perfectly valid current signal can still be decoded to the wrong engineering-unit pressure if the two spans disagree — the built-in check confirms 12 mA decodes to 100 bar when the PLC span is doubled to 200 bar, even though the true process value is 50 bar.
This is a representative educational model with generic parameters: the 12 V minimum transmitter voltage and diagnostic current bands (below 3.6 mA or above 21 mA reads as bad, 3.6–3.8 mA or 20.5–21 mA reads as out-of-range) are teaching settings rather than universal device specifications, and ADC counts saturate at the defined 20 mA full scale rather than modeling a specific converter's resolution.
The transmitter uses a "live zero" convention where 4 mA represents zero process value and 20 mA represents full scale. This lets the loop distinguish a genuinely healthy zero-pressure reading (4 mA) from a broken or de-energized loop, which the model reports as 0 mA with a bad-quality flag.
No — only once the added resistance exhausts the loop's available compliance voltage. The model keeps actual current equal to requested current as long as (Vsupply − 12 V)/(Rwire + Rshunt) can still support it; the built-in check confirms current is unchanged between 0 Ω and 200 Ω of added wire resistance, and only drops once resistance is pushed high enough (for example 1000 Ω) to exceed the available compliance.
The current itself and the PLC's decoding of that current into engineering units are two separate settings. If the transmitter's configured span and the PLC's scaling span disagree, a perfectly valid current — say 12 mA — decodes correctly according to the math but to the wrong physical pressure, which is exactly what the built-in scaling-mismatch experiment demonstrates.
This is a representative educational model with generic parameters rather than a manufacturer-specific device. The 12 V minimum transmitter voltage and diagnostic current bands are teaching settings, the open-loop terminal voltage is shown as available open-circuit voltage, and ADC counts saturate at the defined 20 mA full scale rather than modeling a specific analog input card's resolution.