The OnGuard 4000 is an active corrosion monitor (atmospheric corrosion sensor) made by Purafil.
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Its main function is to continuously monitor corrosion-inducing chemical activity in the air (especially sulfur, chlorine, other corrosive gases) before serious damage happens.
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It tracks the rate of corrosion in real time using sensitive sensors, and also records temperature and relative humidity.
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This helps in:
Characterising the “cleanliness” / corrosivity of an environment
Verifying the performance of molecular filtration (gas filters)
Triggering preventive action if corrosion levels start rising
Ensuring sensitive electronic / instrument equipment are safe from corrosive air
Principle of Operation & Key Features
Some of the key technical details and functional features:
Feature Description / Detail
Sensors Uses Quartz Crystal Microbalance (QCM) sensors, one plated with copper and another plated with silver, to detect the accumulation of corrosion films.
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Measurement units Corrosion is measured and reported in Angstroms (Å) of film growth.
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Correspondence with standards The readings correlate with ISA’s ANSI/ISA-71.04 standard for corrosive environments.
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Maintenance / lifespan The sensors are designed to be replaced when cumulative corrosion reaches ≈ 4000 Å.
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Data & connectivity - On-device interface: backlit LCD + keypad
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- Remote / network: supports Ethernet, SNMP, 4-20 mA output, can be powered by PoE or AA batteries for remote zones
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- Data logging: both incremental (short term) and cumulative corrosion data are stored.
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Accuracy According to the datasheet, accuracy is around ±0.5–1% of span.
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Operating environment The recommended installation environment conditions: temperature from –10 °C to 75 °C, relative humidity 10% to 95% (non-condensing).
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Size / weight Typical physical size: ~ 5.5 in × 1.75 in × 3.5 in (14 cm × 4.5 cm × 9 cm) and weight ~255 g (9 oz)
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Use Cases / Applications
The OnGuard 4000 is suited for environments where corrosion can damage sensitive electronics, instruments, or critical infrastructure. Some example use cases:
Data centers / server rooms / telecom racks
Control rooms / motor control centers
Laboratories / processing rooms
Electronics manufacturing / clean rooms
Any enclosed environment where air filtration is used and one wants to monitor gas-phase contaminants
In these settings, the device can act as an early warning tool to show when corrosion stress is building, or to validate that filtration/gas control is adequate.
