Detcon DM-700 - Manual (Page 15)

Model DM-700
DM-700 Instruction Manual Rev. 4.0 Page 11 of 48
NOTE: If the 4-20mA output is not being used, a 100-250Ω resistor must be installed between
the mA and (-) terminals on the Transient Protection Module to ensure RS-485 communication
is not disrupted by a 4-20mA Fault.
a) If applicable, terminate the RS-485 serial wiring as shown in Figure 10. Use the second plug (Out) as
termination point on the customer side to facilitate a continuous RS-485 serial loop.
The RS-485 (if applicable) requires 24 gauge, two conductor, shielded, twisted pair cable between the sensor
and host. General Cable Commodore part number ZO16P0022189 is recommended.
NOTE: Install a 120-ohm resistor across A & B terminals on the last sensor in the serial loop.
c) Trim all exposed wire leads if they are not permanently landed in the terminal block.
d) Replace the junction box cover.
2.7 Initial Start Up
Upon completion of all mechanical mounting and termination of all field wiring, apply system power in the
range of 11.5-30VDC (24VDC typical) and observe the following normal conditions:
2.7.1 Toxic Gas Sensors
a) DM-700 display reads “0”, and no fault messages are flashing.
b) A temporary upscale or downscale reading may occur as the sensor stabilizes. This upscale reading will
typically decrease to “0” ppm within 1-2 minutes of power-up, assuming there is no gas in the area of the
sensor.
c) Sensors that use a bias voltage require a longer time to stabilize. This can vary between 1 and 24 hours
depending on the sensor type and range. Biased sensors include NH
3
, NO, HCl, and VOC gasses
(ethylene oxide, ethylene, methanol, formaldehyde….etc.).
NOTE: The 4-20mA signal is held constant at 4mA for the first two minutes after power up.
Initial Operational Tests
After a warm up period of 1 hour (or when zero has stabilized), the sensor should be checked to verify
sensitivity to the target gas.
Material Requirements
 Detcon PN 613-120000-700 700 Series Splash Guard with integral Cal Port -OR-
 Detcon PN 943-000006-132 Threaded Calibration Adapter
 Detcon Span Gas; 50% of range target gas in balance N
2
or Air at fixed flow rate between 200-
500cc/min
NOTE: Calibration gas generators using perm tubes or electrochemical sources may be used in
place of span gas cylinders.