You open the case, power it on, and the screen lights up with a number: 20.9%. Now what? The Ntron Yellow Box is a workhorse of portable oxygen measurement across semiconductor cleanrooms, pharmaceutical glove boxes, and heat-treating furnaces — but getting from that first ambient reading to a reliable high-purity measurement depends entirely on how you configure the display and alarms.
The Yellow Box is a portable electrochemical oxygen analyzer built for percent-level O2 measurement in high-purity gas streams. Unlike trace analyzers that chase parts-per-billion, the Yellow Box lives in the 0–100% range where a nitrogen purge, argon blanket, or forming gas mix needs verification that oxygen is either gone or precisely controlled. The front-panel LCD shows real-time O2 concentration, and every configurable parameter — alarm setpoints, analog output scaling, calibration values — is accessible through the four-button membrane keypad.
Navigating the Display Menu
The Yellow Box uses a menu-tree system navigated with four keys: Menu, Up, Down, and Enter. Pressing Menu from the main reading screen enters the configuration menu, where the display cycles through these top-level options:
- ALARM 1
- High or low alarm setpoint in % O2. Factory default is 18.0% for low alarm (confined space entry) but for high-purity applications, set this to your process limit — typically 0.1% or 0.5% — as a low alarm to confirm purge completion.
- ALARM 2
- Second independent alarm. Common practice is to set Alarm 1 as the warning threshold and Alarm 2 as the critical action threshold. For semiconductor gas cabinets, Alarm 2 at 1.0% O2 is typical.
- SPAN
- Span calibration value. The Yellow Box ships calibrated to ambient air (20.9% O2). For high-purity work, span calibration against a certified 100% O2 or 20.9% reference gas is recommended at the start of each shift.
- ZERO
- Zero offset calibration. Use nitrogen (99.999% or better) to set the zero point. In high-purity applications where you are measuring sub-1% O2, a proper zero calibration with N2 is non-negotiable — the electrochemical sensor's baseline drift at the low end is what separates a trustworthy reading from a misleading one.
- 4-20mA
- Analog output scaling. The Yellow Box outputs a 4–20 mA signal proportional to O2 concentration. Default scaling is 4 mA = 0%, 20 mA = 25%. You can remap this to match your PLC or data logger input range.
Can I adjust the display brightness or contrast?
The Yellow Box LCD contrast is factory-set and not user-adjustable through the standard menu. However, the display is a transflective LCD designed for readability in both indoor cleanroom lighting and outdoor daylight — no backlight dependency. If contrast degrades significantly, it typically indicates a low battery condition or aging of the LCD itself, both of which are resolved with a battery replacement or service return to Ntron.
What alarm relay output options does the Yellow Box have?
The Yellow Box includes two user-configurable alarm relays, each a single-pole double-throw (SPDT) contact rated for 24 VDC at 1 A. Each relay can be assigned to Alarm 1 or Alarm 2, and you can configure each as normally energized (fail-safe) or normally de-energized. For glove box purging applications, wiring Alarm 1 as normally energized means a power failure also triggers the alarm — the safer configuration when O2 ingress threatens a batch.
How often should I replace the oxygen sensor?
The electrochemical sensor in the Yellow Box has a typical service life of 18–24 months in ambient air, or 12–18 months in continuous low-O2 service. The sensor depletes faster when exposed to high O2 concentrations (above 30%) for extended periods. Ntron recommends replacing the sensor when the span calibration factor exceeds 150% of the original value — the analyzer will still read correctly after calibration, but a high span factor signals that the sensor electrolyte is depleting and response time is slowing.
How the Yellow Box Compares to Other Ntron Oxygen Products
Ntron builds several fixed and portable oxygen analyzers, and choosing the right one depends on whether you need portability, safety certification, or continuous process monitoring:
- Ntron Yellow Box — portable, percent-level O2, battery-powered, ideal for spot-checking purge integrity across multiple glove boxes or gas cabinets in a shift
- Ntron Gasenz — fixed-mount ambient oxygen monitor designed for personnel safety in labs and gas storage rooms, not for in-line gas measurement
- Ntron Sil02-LT — SIL2-certified oxygen analyzer for safety-instrumented systems in chemical processing, where the analyzer output directly triggers a safety shutdown
- Ntron Senz-Tx — fixed oxygen transmitter with zirconia or electrochemical sensor options, designed for continuous in-line measurement with 4–20 mA output to a PLC or DCS
If you need a portable tool for verifying purge gas purity at multiple points across a facility, the Yellow Box is the right instrument. If you need 24/7 monitoring integrated into a safety system, the Sil02-LT or Senz-Tx is the correct choice. See our full oxygen analyzer catalog for additional portable and fixed O2 measurement options across brands.
