Document Overview
TL;DR Peak Hold and Min/Max functions capture pressure readings that occur faster than a human can read a display — in our T500, the sample rate runs at 200 Hz, meaning the gauge records a new pressure value every 5 milliseconds. If you’ve ever wondered…
- Document type
- Certification Report
- Prepared by
- Kevin Marshall
- Published
- Last reviewed
- Topics
- Digital Gauges
TL;DR
Peak Hold and Min/Max functions capture pressure readings that occur faster than a human can read a display — in our T500, the sample rate runs at 200 Hz, meaning the gauge records a new pressure value every 5 milliseconds. If you’ve ever wondered why your tire pressure reads differently during inflation versus after you remove the chuck, these functions explain exactly what’s happening and why they matter.
How Peak Detection Works: Sample Rate and Display Logic
A digital pressure gauge isn’t continuously displaying raw sensor output. What you see on the LCD is a processed value — filtered, averaged, and updated at a display refresh rate that’s typically 2–5 Hz for readability. The underlying sensor, however, samples far faster. In the T500, the piezoresistive MEMS sensor polls at 200 Hz continuously. Peak Hold and Min/Max functions operate on that raw 200 Hz data stream, not on the display-rate output.
Peak Hold logic is straightforward: the firmware maintains a register that stores the highest pressure value seen since the function was activated. Every new sample is compared against the stored peak. If the new value exceeds the stored value, the register updates. The display then shows the stored peak value rather than the live reading. This captures transient pressure spikes that would otherwise vanish before the display refreshes.
Min/Max extends this by maintaining two registers simultaneously — one tracking the floor, one tracking the ceiling. This is particularly useful when monitoring pressure behavior over a fill cycle, where you want to know both the settled minimum at the start and the peak reached during inflation.
The engineering challenge in implementing these functions isn’t the register logic — that’s trivial. The challenge is noise discrimination. A raw 200 Hz pressure signal contains sensor noise, typically ±0.3 PSI peak-to-peak on a MEMS sensor at 100 PSI. Without filtering, every noise spike would register as a new peak. We apply a 5-sample moving average to the 200 Hz stream before feeding it to the peak detection register. This keeps noise below ±0.15 PSI while preserving genuine transient events down to approximately 25 milliseconds duration. That tradeoff — noise suppression versus transient capture speed — is what separates a well-engineered peak hold from a marketing checkbox.
For the underlying sensor calibration standard, see ANSI Standards for ANSI B40.7, which defines accuracy grades for pressure gauges. Our implementation targets Grade 2A accuracy (±1% of full scale) across the functional range, verified against a NIST-traceable reference standard during final QC. For a full breakdown of what those accuracy grades mean in practice, see our article on Understanding ANSI B40.7 Accuracy Grades for Digital Tire Pressure Gauges.
Why Sample Rate Determines Whether Peak Hold Is Useful
A common question from technical buyers: “What sample rate is actually necessary for tire pressure applications?” The answer depends on what event you’re trying to capture.
Chuck connection spike. When you attach an inflator chuck to a tire valve, there’s a brief pressure equalization event between the hose line and the tire. Depending on hose volume and line pressure, this spike can last 50–150 milliseconds and reach 5–15 PSI above tire pressure before settling. At a 2 Hz display refresh rate (500 ms per update), this spike is invisible. At 200 Hz (5 ms per sample), it’s captured cleanly.
Inflation overshoot. Auto-stop inflators — even well-tuned ones — have control loop latency between detecting target pressure and closing the valve. During that window, pressure can overshoot by 1–4 PSI. Peak Hold quantifies this overshoot precisely, which matters if you’re inflating to within tight tolerances (for example, track tire setups at 32.0 PSI ±0.5 PSI). For more on how auto-stop control loops work, see Understanding Auto-Stop Pressure Control in Tire Inflators.
Leak testing. The Min function is the relevant one here. Connect the gauge to a pressurized system and activate Min tracking. Over a 2–5 minute observation window, any pressure loss registers as a new minimum. This gives you a quantified leak rate (PSI/minute) rather than a subjective judgment about whether the needle moved.
| Use Case | Relevant Function | Minimum Useful Sample Rate | Observable Event Duration |
|---|---|---|---|
| Chuck connection spike | Peak Hold | ≥ 50 Hz | 50–150 ms |
| Auto-stop overshoot | Peak Hold | ≥ 20 Hz | 100–400 ms |
| Inflation overshoot at target | Peak Hold | ≥ 20 Hz | 100–500 ms |
| Slow leak detection | Min Hold | ≥ 1 Hz | Minutes |
| Thermal pressure rise monitoring | Min/Max | ≥ 1 Hz | Minutes to hours |
| Track tire pressure management | Min/Max | ≥ 10 Hz | Varies |
We chose 200 Hz for the T500 not because every use case demands it, but because the MEMS sensor we selected runs natively at that rate and the MCU has the headroom to process it without impacting display response time. Downsampling to a lower rate would have required additional firmware complexity for no gain in battery life — the sensor draws the same current regardless of whether we read it at 10 Hz or 200 Hz.
The industry context here matters: most budget digital gauges in the $8–$15 range use resistive or strain-gauge sensors sampled at 10–20 Hz with no dedicated peak hold logic. Their “peak hold” feature (if present) simply latches the display refresh value, which means they’re capturing a 2 Hz snapshot labeled as “peak.” That’s not peak detection — it’s display freeze. SAE International has published test procedures (SAE J1061) for tire inflation equipment that touch on measurement response requirements, which is part of why we hold the T500 to a higher engineering standard than the minimum market expectation.
T500 Implementation: Design Decisions and Test Data
We made three specific design decisions in the T500 that affect how Peak Hold and Min/Max behave in field use.
Automatic reset on unit power cycle, manual reset during session. Some gauges reset peak registers every time you take a new reading. We found in user testing that this makes Peak Hold useless for sequential tire checks — you’d lose the peak from tire 1 when you moved to tire 2. The T500 retains peak values until you explicitly press the reset button or power off the unit. This means you can check all four tires and review the Min/Max spread across the session, which is useful for diagnosing uneven pressure distribution.
Display mode toggling with 500 ms hold. We debated whether to use separate buttons for Live, Peak, and Min/Max display modes. The conclusion was that adding buttons increases ingress risk points on the housing (each button requires a gasket seal) and creates confusion for infrequent users. A single 500 ms button hold cycles through display modes: Live → Peak → Min → Max → Live. The current mode indicator occupies the upper-left corner of the LCD using a dedicated segment, so there’s no ambiguity about what value you’re reading.
Peak register resolution matches sensor resolution: 0.1 PSI / 1 kPa. Some implementations store the peak at display resolution (which might be rounded to 0.5 PSI). We store peak values at full sensor resolution. This matters for the inflation overshoot use case — a 0.3 PSI overshoot is meaningful data if you’re tuning a high-pressure bicycle tire at 110 PSI, and rounding it to 0.5 PSI increments would mask it entirely.
For test data: in our thermal cycling validation, we ran the T500 through 50 measurement cycles at 25°C ambient, sampling Peak Hold accuracy against a deadweight tester at pressures of 15, 35, 60, and 100 PSI. Peak Hold register values matched the reference within ±0.5% of reading across all test points — within the ANSI B40.7 Grade 2A specification of ±1% full scale. Below -5°C, we observed that LCD segment response time increased from 12 ms to approximately 35 ms, but peak register accuracy was unaffected because the register operates on MCU memory, not on display hardware. This is the same thermal behavior documented in the T600 — for a full comparison of the T600’s display behavior, see Etenwolf T600 Digital Tire Pressure Gauge: Accuracy & Usage Guide.
RoHS compliance for the T500 PCB and display assembly is documented under EU RoHS Directive 2011/65/EU, restricting hazardous substances in electrical equipment. CE marking covers the full EU declaration of conformity — verified through EU CE Marking procedures.
Maintenance & Best Practices
Peak Hold and Min/Max functions place no additional mechanical stress on the gauge — they’re purely firmware features operating on sensor data. That said, a few practices keep the underlying measurement chain accurate enough for these functions to be meaningful.
Zero-check monthly. With the gauge disconnected from any pressure source and the chuck open to atmosphere, the live reading should display 0.0 PSI (or within ±0.15 PSI). If it reads ±0.5 PSI or more at zero, the sensor baseline has drifted and peak hold values will carry that offset error into every reading.
Avoid chuck-on storage. Storing the gauge with a chuck adapter attached to the port traps moisture. Over time, moisture ingress can shift the piezoresistive sensor’s baseline output. Store with the port cap in place.
Reset peak registers before each session. Leaving stale peak values from a previous session active leads to confusion — particularly if the previous session involved a different pressure range (for example, switching from car tires at 35 PSI to a bicycle at 100 PSI). Make it a habit to press-and-hold reset before beginning any new measurement session.
Check the button seal annually. The mode/reset button is the primary ingress point on the T500 housing. If the button feels sticky or requires more force than usual, the silicone gasket behind it may be compressed or contaminated. Clean the button perimeter with isopropyl alcohol on a cotton swab.
Battery voltage affects sensor accuracy below 2.4V. The T500 MEMS sensor requires a stable 3.0V regulated supply. The internal LDO regulator maintains this down to a 2.4V battery input. Below that, peak hold values may read 1–2% high due to reference voltage sag. Replace the CR2032 cell when the low-battery indicator appears — don’t push through it on measurement-critical work.
Frequently Asked Questions
Q1: What is Peak Hold on a digital tire pressure gauge and when should I use it?
A: Peak Hold captures the highest pressure value recorded since the function was activated, even if that peak lasted only milliseconds. Use it when connecting an inflator chuck (to see the equalization spike), when checking auto-stop overshoot, or any time you need to know the maximum pressure reached during a fill cycle.
Q2: How is Min/Max different from Peak Hold, and which is more useful for leak testing?
A: Peak Hold only tracks the highest value. Min/Max tracks both the highest and lowest pressure recorded in a session. For leak testing, Min is the relevant function — connect the gauge, activate Min tracking, and monitor the minimum value over 3–5 minutes. A pressure drop of more than 0.5 PSI per minute on a passenger tire at 35 PSI indicates a leak worth investigating. Peak Hold alone won’t show you this because it ignores pressure decreases entirely.
Q3: Does the sample rate of a digital gauge affect Peak Hold accuracy?
A: Yes, significantly. A gauge sampling at 2 Hz (once every 500 ms) can completely miss transient pressure spikes shorter than 500 ms — including chuck connection spikes and auto-stop overshoot events, both of which typically last 50–400 ms. The T500 samples at 200 Hz, capturing events as short as 25 ms after filtering. If a gauge’s spec sheet doesn’t list a sample rate, assume it’s running display-refresh-rate peak detection, not true high-speed peak capture.
Q4: Is the T500’s Peak Hold function validated to any measurement standard?
A: Peak Hold register accuracy is validated as part of our ANSI B40.7 Grade 2A testing protocol, where peak values are compared against a deadweight tester reference traceable to NIST. The underlying measurement accuracy standard is ANSI B40.7, published by ANSI Standards. Every production T500 is verified on this test rig before shipping.
Q5: Can Peak Hold show me whether my inflator is overshooting the target pressure?
A: Exactly what it’s designed for in this context. Set your target pressure, run the inflator to auto-stop, then check the Peak Hold value. The difference between Peak and the settled live reading is your overshoot. On a well-tuned inflator with fast valve response, this should be under 2 PSI. If you’re seeing 4–6 PSI of overshoot consistently, the inflator’s pressure control loop has too much latency — either the sensor is slow or the valve actuation is delayed. This kind of diagnostic isn’t possible without a gauge that captures sub-second peak values.
Published by ETENWOLF Technical Team | Request a quote