Honeywell Design and Application Technical Reference Manual page 167

The sensor now contains the algorithm and
will send either a 4mA OR a 20 mA signal to
the economizer where 4mA is NOT OK to
economize and 20mA is OK to economize.
For example if the operator selects a 73F
change over, the sensor will send a 20 mA
signal to the logic module at 72F and below
and will send a 4 mA signal to the logic
module at 74F and above.
The C7660 can only be used in referential
mode or single dry bulb only, it cannot be used
in differential dry bulb mode. If you are using
differential mode it is recommended to use two
of the C7650 sensors.
The legacy economizer modules are all
provided with sensor connections for either a
mixed or supply air sensor input to modulate
the mixed air dampers. Either the C7046A or
Section 12 - Sensors for Economizer Modules
C7150B can be used for this function since the
resistance curves for both are identical. The
C7046A is 8 inches (20 cm) long which makes
it a better selection for larger air handlers than
the single point C7150B. When installing the
C7150B use a simple smoke bomb to
determine air flow and locate the sensor in a
location where the OA and RA have the best
mix. Do not use a smoke bomb in an occupied
building.
The DCV economizer modules can be used
with any indoor air content sensor with a 0 or 2
to 10 Vdc output. For most indoor applications
Honeywell C7232 or C7632 carbon dioxide
sensors will be used. They are available in
either wall or duct mount versions with or
without display.
161 Honeywell Economizers 63-8594-02