1
MACURCO GAS DETECTORS
ND-1
INSTALLATION & OPERATING INSTRUCTIONS
WWW.MACURCO.COM
GENERAL INFORMATION
The ND-1 is a microcomputer controlled electronic sensor and controller for Nitrogen Dioxide (NO
2
). The
unit has a NO
2
sensor (electrochemical), digital display, status lights, buzzer and relays. Please see the ND-1 data
sheet for more detailed information.
LOCATION
The unit, on average, can cover about 5000 sq. ft. (465 sq. meters). The coverage depends on air movement in
the room or facility. Extra detectors may be needed near any areas where people work, or the air is stagnant.
Normally, the unit mounts 5 feet (1.5 meters) above the floor in a central area where air movement is generally
good. See the ND-1 data sheet for more information on location.
INSTALLATION
The
ND-1 is housed in an electrical box that has mounting holes on the back. Conduit can be connected to the
bottom three knock-out holes. Do NOT remove the four black vents in the case. They are necessary for adequate
air flow into the unit. Remove the two small screws toward the
bottom
of the inside cover. The inside cover then
swings up for access to internal circuitry.
Once the cover is open, you should notice a seven-screw terminal block. The first two screws, at the far left,
are for power and are marked “POWER 12-24 V ac/dc”. There is no polarity. The three middle terminals are for
the Fan SPDT relay. They are marked from left to right N.O. (normally-open), COM (common), and N.C.
(normally-closed). The Fan relay contacts can handle up to 5 amps. The two terminals at the far right are for the
Alarm relay. They are both marked N.O. (normally-open). The Alarm relay contacts can handle up to 0.5 amps.
The relays have dry contacts. See the ND-1 data sheet for detailed schematics on wiring and other technical
information.
OPERATION
When power is first applied to the detector, it will go through a warm-up period of 30 seconds. The digital
display will count down from 30 to 0 during the warm-up period. The Fan and Alarm relays will also actuate
during the warm-up period.
The ND-1 is now operational. Set the Fan and Alarm PPM levels as needed for the job requirements. The
current OSHA and ACGIH values for
NO
2
are TWA of 3 ppm (parts per million) and STEL of 5 ppm. The
suggested settings to meet those limits are a Fan setting of 3 ppm and an Alarm setting of 5 ppm.
The Fan turn-on delay can be set from 0 to 5 minutes by setting the 3-segment “FAN DELAY” switch (inside
the unit just below the big blue buzzer). When the turn-on delay has been actuated by the NO
2
level exceeding the
threshold settings, the amber light will flash. When the turn-on delay is over the amber light will come on solid
and the Fan relay will actuate.
FAN DELAY SWITCH CHART
NONE 30 SEC. 45 SEC. 1 MIN. 2 MIN. 3 MIN. 4 MIN. 5 MIN.
The Alarm turn-on delay (flashing red) is fixed at 5 minutes. A solid red light indicates Alarm relay
activation, and the buzzer will sound. Both Fan and Alarm relays have a minimum on-time of 30 seconds. This is
to prevent short cycling devices connected to the relays.
TESTING
Testing the unit can be done by pressing the “TEST” switch located near the buzzer on the printed circuit
board. This will initiate the test cycle. The display will read 88.8, both the Fan and Alarm relays will actuate,
both Fan and Alarm status lights will be on solid, and the buzzer will sound. The test cycle will last approximately
30 seconds.
