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page 3
1 Introduction
NanoSense produces since nearly twenty years’ air quality probes with modular architectures for
sensitive elements that can be changed (after approximately 10 to 15 years) in order to extend the life
of the product and keep the initial setting. A BIT (Built In Test) allows to identify most of defaults via LEDs
alerts.
On the EP5000 range, the BIT is associated to a BITE (Built In Test Equipment) which identifies the
defective replaceable unit in order to facilitate on-site maintenance and reduce downtime.
2 Principle
The probe motherboard has a built-in test function for each FRU (Field Replaceable Unit) with a status
report via digital communication and the LED interface.
Each replaceable unit is designed to be a FRU.
In case failure, each item can be ordered from the manufacturer and replaced by a technician or even a
qualified end user in accordance with this repair manual.
IAQ sensors with a lifespan of 10 to 15 years are pluggable and considered as FRU: Particles, CO2, VOC.
Most of other sensors are digital MEMS sensors soldered on the boards with an unsignificant drift over
the life of the probe or FRU.
Board organization is made by function and each one is a FRU.
Changing a FRU requires only a simple screwdriver.
Mechanical parts are also FRU s and can be ordered separately as part of the repairability and durability
policy. See the list of FRU in the appendix.
3 Identification of defective FRU
At the first start-up, the probe interrogates and identifies all the sensors, memories and radio transceiver
present then compare with the configuration of the product and records data in a table. The supply
voltages are also checked and compared to required nominal values.
The Built In Test (BIT) identifies failures and BITE (Built In Test Equipment) identify the defective FRU to
change by comparing the array of elements present and those that no longer respond. If the supply
voltages do not meet the specifications, the power supply board is declared defective. However, this test
is not entirely foolproof because an abnormal overconsumption of a component could be the cause but
it is impossible to have a BIT/BITE which covers 100% of failures. However, overheating can be suspected
when the internal temperature measurement of the microcontroller is too far from the ambient
measurement. In the event of a total failure of the power supply board, the microcontroller being no
longer supplied with power, it is impossible to perform a self-test. We must therefore base ourselves on
the non-activation of the LEDs on the front panel and or no data transmission.
