Digital Panel Meter for Duty Cycle and Pulse Width Modulation (PWM) Applications P/N L71015FR

Duty Cycle & PWM Digital Panel Meter Frequently Asked Questions

Why is the same physical signal applied to both Channel A and Channel B for duty cycle measurement, rather than using two separate signals?

Duty cycle calculation specifically requires both the pulse width (t) and the full period (P) from the same waveform to compute their ratio — applying the identical signal to both channels lets the meter derive both quantities from a single source simultaneously, rather than needing a second independent signal the way true A-B time-interval measurement would.

Does selecting the leading edge versus falling edge for duty cycle measurement change the underlying period being measured, or only which portion is reported as "ON"?

Only which portion is reported — the underlying period P (the full repeating cycle) stays the same regardless of edge selection; choosing leading versus falling edge specifically determines whether the meter reports the high-time or low-time portion of that same cycle as the duty cycle percentage, giving ON duty cycle or OFF duty cycle from the identical underlying waveform.

Why does accuracy degrade from 0.01% at low frequencies to 1% at 10 kHz for both duty cycle and PWM modes identically?

Since PWM mode is documented as using the same underlying duty-cycle-ratio calculation as duty cycle mode (simply scaled afterward into engineering units), both modes share the identical underlying timing measurement and therefore the identical accuracy-versus-frequency behavior — the engineering-unit scaling applied in PWM mode happens after the core timing measurement, so it doesn't introduce a separate accuracy degradation of its own.

Does PWM mode require the transducer's constant carrier frequency to be manually entered into the meter, or does the meter detect it automatically?

The meter is documented as measuring the actual period between pulses directly from the incoming signal rather than requiring a manually entered assumed frequency — since duty cycle is calculated as the ratio of pulse width to the actually measured period, the meter inherently tracks the real incoming carrier period rather than depending on an independently configured frequency value.

In the laser monitoring application, is total energy calculated internally by the meter, or does it require external computation from the transmitted duty cycle and pulse data?

Documented capability specifically lists total energy applied as one of the values Laureate counters can directly display and transmit alongside duty cycle, pulse count, elapsed time, and average pulse width — meaning this calculation is documented as performed internally by the meter itself, rather than requiring separate external computation from the other transmitted values.

Can duty cycle and PWM measurement be performed simultaneously with the Extended board's other listed functions, such as phase angle or frequency, on the same meter at the same time?

No — documented capability specifically describes the Extended counter board as supporting all of these functions (duty cycle, PWM, time interval, stopwatch, frequency, rate, phase angle, and more) as available operating modes on the same hardware, meaning the meter operates in one selected mode at a time rather than running multiple of these functions concurrently on a single instrument.

Does selecting a shorter gate time in duty cycle mode risk capturing an unrepresentative single cycle rather than a genuinely averaged reading?

The documented averaging mechanism specifically integrates over "an integral number of periods" within the selected gate time — a very short gate time could reduce that integral number down toward a single period, which would indeed reduce the averaging benefit; selecting a gate time comfortably longer than one signal period is what ensures genuine multi-cycle averaging rather than an effectively single-cycle reading.

Does the meter's own accuracy specification account for jitter or noise already present on the incoming PWM signal, or only its own internal measurement accuracy?

The documented accuracy figures describe the meter's own internal measurement accuracy under its stated conditions — they don't separately characterize or compensate for noise or jitter genuinely present on the incoming signal itself, meaning a noisy source signal can still produce reading variation beyond the meter's own documented accuracy specification, addressable through the meter's selectable noise filter and digital filtering options.

Does the meter's Time Before Zero Out setting behave differently in duty cycle mode compared to how it's used in frequency or rate modes?

The documented mechanism itself is the same across modes — a separately selectable 10 ms to 199.99 s window that zeros the display if no valid new signal is detected — but in duty cycle mode specifically, this matters for detecting a PWM or duty-cycle source that has stopped pulsing entirely, distinguishing a genuine loss-of-signal condition from a valid but very low duty cycle reading that's still actively updating.

Can the analog output board retransmit a PWM-scaled engineering-unit reading the same way it retransmits a raw duty cycle percentage?

Yes — since PWM mode's engineering-unit value is documented as the same underlying t/P ratio simply scaled mathematically after calculation, the analog output board (which tracks whatever value the meter is currently configured to display) retransmits that scaled PWM reading the same way it would retransmit a raw duty cycle percentage, without requiring separate analog-output configuration logic for the two modes.

PWM Dead-Time & Shoot-Through Prevention Questions From the Field

What is "shoot-through," and why is it specifically a risk in PWM-driven H-bridge motor or solenoid control circuits?

Documented explanation specifically describes shoot-through as a short circuit condition where both the high-side and low-side switching devices on the same H-bridge leg conduct simultaneously, creating a direct low-impedance path from supply to ground — this is documented as capable of destroying the switching transistors and causing substantial current spikes, making it a genuine, damage-risk failure mode rather than just a performance inefficiency.

What specifically is "dead time," and how does it prevent shoot-through in a PWM motor drive?

Documented technique specifically describes dead time as a deliberately inserted buffer period between when one switching device turns off and when its complementary device turns on within the same H-bridge leg — by ensuring the two devices are never both actively conducting at the same instant, this timing gap specifically prevents the shoot-through condition from occurring.

Is dead time typically implemented in hardware, firmware, or both?

Documented practice specifically describes both approaches as commonly used — dedicated dead-time generator circuits exist as a hardware solution, while it's also documented as commonly implemented in firmware, where advanced microcontroller timers generate the desired dead-time gap between complementary PWM signals without requiring separate dead-time hardware.

Is there a documented typical range for dead-time duration in PWM motor control circuits, and does that duration depend on the switching devices used?

Yes — documented guidance specifically cites typical dead-time values around 100-300 nanoseconds for silicon MOSFETs, with the general documented principle that minimum dead time should exceed the slowest switching device's maximum turn-off time plus a safety margin; faster or slower switching devices genuinely require correspondingly shorter or longer dead-time settings.

Does adding more dead time than strictly necessary provide extra safety margin with no real downside?

No — documented analysis specifically notes that excessive dead time reduces the effective output voltage delivered to the load and increases output ripple, meaning dead time involves a genuine tradeoff between shoot-through safety margin and control precision, rather than being a setting where "more is simply safer" without cost.

Can a PWM drive circuit experience shoot-through even with dead-time circuitry correctly implemented, under any documented conditions?

Yes — documented analysis of one specific dead-time-free H-bridge driver design specifically identifies a scenario where one input holds a constant high state while the other is separately controlled by PWM, noting this specific combination can still cause shoot-through even in designs otherwise built to avoid needing dead-time circuitry — illustrating dead-time protection isn't automatically foolproof against every possible signal combination.

What documented real-world symptom can indicate a PWM H-bridge circuit is suffering from inadequate dead time or a missing interlock?

Documented field troubleshooting specifically describes an audible "whine" from the circuit board when powered as the bench symptom of a free-running drive signal chain lacking an enforced dead-time interlock — this specific audible signature is documented as a practical diagnostic clue pointing toward a shoot-through-prone design before it necessarily causes visible component damage.

Does synchronous PWM switching (actively driving both high-side and low-side devices) require dead-time protection the same way as simpler PWM schemes?

Yes, and arguably more critically — documented comparison specifically notes synchronous PWM switching reduces power dissipation by conducting current through the MOSFET channel rather than a body diode, but explicitly requires dead-time insertion to prevent shoot-through as a consequence of actively switching both devices, whereas simpler schemes leaving one device always on avoid this specific requirement at the cost of higher losses through the body diode.