Panel Meters for Duty Cycle and Pulse Width Modulation (PWM) Applications P/N L7002DFR

Duty Cycle & PWM Panel Meter Frequently Asked Questions

Why does the meter apply the same signal to both Channels A and B for duty cycle measurement instead of using separate channels?

Duty cycle inherently requires comparing a pulse's active-time portion against its total period from the same single waveform — since both the pulse width and the overall period come from the identical signal, feeding it to both channels lets the meter's dual-channel processing derive both the numerator (pulse width t) and denominator (period P) of the t/P ratio from one physical connection rather than needing two separate signal sources.

What's the actual difference between "duty cycle mode" and "PWM mode" if both compute the same t/P ratio?

The underlying ratio calculation is documented as identical between the two modes — the distinction is what happens after that ratio is computed: duty cycle mode displays the raw percentage directly, while PWM mode takes that same ratio and mathematically scales it into different engineering units (such as relative humidity) appropriate for whatever physical quantity the transmitter is encoding via its PWM output.

Why would a PWM transducer use a fixed carrier frequency like 120 Hz instead of encoding information in the frequency itself?

Documented PWM transducer design specifically separates the carrier frequency (fixed, such as 120 Hz) from the information-carrying element (the duty cycle ratio) — keeping the frequency constant simplifies the receiving meter's job, since it only needs to track the changing ON/OFF ratio at a known, stable rate rather than simultaneously tracking a variable frequency and a variable duty cycle together.

Does selecting leading versus falling edge actually change the underlying measurement, or just which portion of the cycle is reported?

Just which portion is reported — since ON time and OFF time together make up the full period, selecting leading or falling pulse edges determines whether the meter reports the ON-time percentage or the OFF-time percentage of that same cycle; the underlying period and pulse timing being measured don't change, only which complementary percentage is calculated and displayed.

Why does accuracy degrade from 0.01% at low frequencies to 1% at 10 kHz, rather than staying constant across the full range?

This reflects the practical limits of timing resolution relative to signal period — at low frequencies, each cycle's period is long relative to the meter's underlying timing resolution, so the pulse-width-to-period ratio can be measured very precisely; at 10 kHz, each cycle is much shorter, leaving proportionally less time resolution available within each individual cycle to pin down the t/P ratio as precisely, which is why accuracy documented at 10 kHz is coarser than at low frequencies.

Can this same meter be reconfigured from duty cycle/PWM mode into, say, a stopwatch or frequency meter without buying new hardware?

Yes — the Extended counter main board is documented as supporting all of these modes (A-B time interval, stopwatch, frequency, rate, period, square root of rate, totalizing, arithmetic functions, phase angle, batching, custom curve linearization) on the same physical hardware; switching between them is a setup/configuration change via the front panel or setup software, not a hardware swap.

Does monitoring total energy applied in the laser application require a separate power meter, or does the Laureate counter compute it directly?

Documented capability specifically lists total energy applied as one of the parameters the Laureate counter itself can display, alongside duty cycle, pulse count, elapsed time, and average pulse width — this suggests the counter performs this calculation internally from the timing and pulse data it's already measuring, rather than requiring an entirely separate power/energy measurement instrument.

Can the laser monitoring data (duty cycle, pulse count, energy, etc.) be logged remotely, or does it require someone reading the front panel display?

It can be logged remotely — documented capability specifically states this data can be transmitted digitally via RS485 or Ethernet, meaning a connected data logger, SCADA system, or networked PC can capture and record these laser operating parameters continuously without requiring an operator to manually read and record the front panel display.

Does the meter's contact debounce and noise filter settings apply to duty cycle/PWM mode the same way they do in other counter modes?

Yes — since duty cycle and PWM measurement rely on the same underlying pulse-edge detection circuitry used across the Laureate counter's other modes, the selectable noise filter (1 MHz, 30 kHz, or 250 Hz) and contact debounce (0, 3, or 50 ms) settings apply here as well, letting the meter be tuned for a genuinely noisy PWM source (such as a long cable run picking up interference) the same way it would be tuned for a noisy frequency or rate signal.

Can the analog output board retransmit the measured duty cycle or PWM reading as a 4-20 mA or 0-10V signal to another system?

Yes — the optional analog output board is documented as available across the Laureate counter family generally, and since duty cycle/PWM is simply one of the meter's selectable operating modes on the same underlying hardware, the currently displayed duty cycle or scaled PWM reading can be retransmitted as 4-20 mA, 0-20 mA, or 0-10V for use by an external controller, recorder, or SCADA system, the same as it would for any other mode's reading.

PWM Frequency Selection: Audible Noise & Switching Loss Questions From the Field

Why does a motor driven by PWM sometimes produce an audible whine, and what does frequency have to do with it?

Documented analysis specifically explains that any PWM frequency within the human audible range (roughly 20 Hz to 20 kHz) causes the motor's windings and iron core to physically vibrate at that switching frequency, and that vibration transmits as audible noise — a common default PWM frequency like ~490 Hz sits squarely in this audible range, which is documented as a frequent source of unwanted motor whine in real designs.

If raising PWM frequency above the audible range eliminates motor whine, why not always default to a very high frequency?

Documented engineering tradeoffs specifically warn against this — switching losses in MOSFETs and similar switching devices increase roughly proportionally with frequency, meaning doubling the PWM frequency roughly doubles switching losses, which raises device temperature and can reduce overall system efficiency; a documented example shows a MOSFET temperature increase of about 15°C when frequency was raised from 20 kHz to 40 kHz specifically to eliminate noise.

Is there a documented "sweet spot" frequency range commonly recommended for DC motor PWM control?

Yes — documented guidance commonly cites roughly 15-20 kHz as a frequently chosen range for DC motor control, specifically because it sits above most of the audible range while avoiding the more severe switching losses associated with much higher frequencies; some sources note smaller motors or micro-actuators may benefit from even higher frequencies (above 10 kHz) given their different inductance characteristics.

Does LED PWM dimming face the same audible-noise concern as motor control, or is that specific to motors?

LEDs themselves are documented as facing a related but distinct audible noise mechanism — the noise in LED dimming applications is documented as originating from ripple current interacting with system components like output capacitors and power rails, particularly with large LED currents or multiple LED strings, rather than mechanical vibration of windings the way it occurs in motors, though the practical mitigation (shifting frequency above 20 kHz) is documented as a comparable solution.

Why is shifting PWM frequency above 20 kHz to eliminate audible noise sometimes described as "not always desirable" despite solving the noise problem?

Documented tradeoff analysis specifically identifies two consequences of this approach: increased switching losses (reducing system power efficiency) and greater electromagnetic interference (EMI) generation at higher switching frequencies — meaning eliminating audible noise this way can trade one engineering problem (acoustic noise) for others (thermal/efficiency and EMI compliance issues) that must be separately managed.

Does the minimum PWM frequency needed to avoid visible flicker in LED dimming applications differ meaningfully from the frequency needed to avoid audible motor noise?

Yes, documented guidance shows these are governed by different physical thresholds — visible flicker in LED dimming is documented as becoming perceptible below roughly 60-100 Hz depending on viewing conditions, with LED dimming commonly using 200 Hz to 2 kHz to comfortably clear that threshold, which is a substantially lower frequency range than the 15-20+ kHz commonly used specifically to avoid audible motor whine.

For a slow-responding load like a resistive heater, does PWM frequency selection face the same audible-noise/switching-loss tradeoff as motors and LEDs?

No, documented guidance specifically notes this case is different — because heaters respond slowly to power changes, even quite low PWM frequencies (documented as roughly 10-100 Hz) are sufficient to provide stable, effective temperature control, meaning heater PWM applications generally don't face the same pressure toward high frequencies that motor or LED audible-noise concerns create.

Does increasing PWM resolution (more duty-cycle steps) come with a tradeoff against frequency, or are they independent design choices?

They're documented as directly linked, not independent — since resolution is tied to how many discrete duty-cycle steps fit within one PWM period at a given underlying clock rate, documented guidance specifically notes that increasing resolution generally requires lowering the maximum achievable PWM frequency (or vice versa) for a fixed clock source, meaning a designer genuinely has to balance fine duty-cycle control against how high a frequency the system can practically achieve.