2
I) SYSTEM DESCRIPTION
Conspec’s P2621-NO2/VC Nitrogen Dioxide (NO2) Monitor / Ventilation Controller is
designed for use where ventilation fans are installed to prevent the accumulation of
dangerous levels of Nitrogen Dioxide. Nitrogen Dioxide is a toxic byproduct of
combustion and is contained in the exhaust of internal combustion engines. The P2621-
NO2/VC utilizes a programmable micro-Controller combined with a high-quality electro-
chemical Nitrogen Dioxide sensor to measure the NO2 level from 0-20ppm. The P2621-
NO2/VC displays the NO2 level on the built-in LCD display, and activates a fan relay to
ventilate the area when elevated concentrations (1 ppm) of NO2 are detected. The
P2621-NO2/VC’s audible alarm sounds if the NO2 level remains at an elevated level (3
ppm) for more than 15 minutes to signal nearby persons to leave the area. The P2621-
NO2/VC continually self-tests the internal electronic circuitry and the sensor, and signals
if a fault is detected. Front-panel LED indicators are provided for “Power”, “Fan (ON)”,
“Alarm”, and “Fail”. The P2621-NO2/VC is factory tested and calibrated prior to
shipment. Field calibrations are possible with the optional P1879-NO2 Calibration Kit
and P2621-H handheld programmer module. The P2621-NO2/VC operate on 24VAC
power and consumes less than .15W max.
The P2621-NO2/VC’s “Fan” relay is operated in the failsafe mode where the relay coil
is energized whenever the P2621-NO2/VC is in a non-alarm condition and the normally-
open contact (terminal connections K1 & K2) is held closed. When any fault occurs the
“Fan” relay is de-energized and the normally-open contact (terminal connections K1 &
K2) falls open. The “Fan” relay is de-energized at start-up, when the NO2 level rises
above 1ppm, when the internal diagnostics program detects a fault or when AC power to
the unit is lost. The “Fan” relay is re-energized when the fault is cleared. The P2621-
NO2/VC’s programming holds the “Fan” relay de-energized for a minimum of three
minutes once activated to prevent short-cycling of the exhaust fans.
The P2621-NO2/VC’s optional “Alarm” relay (terminal connections K3 & K4)
operates on the same principle as the internal audible alarm. The audible alarm is
activated only after the NO2 level has exceeded 3ppm for 15 minutes. The audible alarm
(and optional “Alarm” relay) deactivate when the NO2 level drops below 3ppm.
II) POWER REQUIREMENTS
Warning: The use of the P2621-NO2/VC unit with higher or lower voltages can
damage the unit and cause improper operation or a hazardous condition.
The P2621-NO2/VC was engineered to be used with 24VAC power supply and a 24
VAC relay control circuit. The relay contacts are rated 5A@ 24VAC for use with an
inductive load. If the installation requires a higher voltage or greater load capacity,
replace the relay unit with an appropriately rated relay (or use a second relay between the
control relay and the load). Power requirements for each P2621-NO2/VC are 24 VAC at
0.5 amps.
