Cambridge Air Solutions
40
SA-Series Technical Manual
GAS CONTROL COMPONENTS
AMPLIFIER (AMP)
The amplifier creates a voltage output to
drive the modulating valve to maintain
the selected discharge temperature.
For EDL Mode, the discharge
temperature is set at the amplifier.
For EDSM Mode, the range of the
discharge temperature is set at the
amplifier, however, the adjustable temperature selector
controls when more or less heat is required.
COMBINATION VALVE
The combination valve serves as a
manifold pressure regulator and
redundant gas shut-off valve. The valve
operates on 24 Volts AC power. The
combination valve is rated for a
maximum gas supply pressure of 14"
WC.
DISCHARGE AIR TEMPERATURE
SAMPLING BOX
The discharge air temperature sampling
box is located on the side of the
discharge, and is accessible from the
electrical control enclosure side of the
unit. The sampling box houses the high
limit and the DTS. This box should not
be tampered with unless performing
the Calibration Procedures (page 17).
DISCHARGE TEMPERATURE SENSOR
(DTS)
The DTS is mounted in the discharge of
the heater. It senses the average discharge
temperature and transmits a resistance
signal back to the amplifier that
corresponds to the discharge temperature.
FLAME ROD (FR)
The flame rod senses the presence of flame
and signals the flame safeguard relay. The
presence of flame is detected by the flame
rectification of the AC signal that is
supplied to the flame rod thus creating the DC response.
The resulting current flow produced can be measured
with a DC microammeter. The reading should be steady
and between 2.0 and 6.0 microamps (
μ
A
)
.
FLAME SAFEGUARD RELAY (FSR)
The flame safeguard relay supplies 24
Volts AC to the igniter for 4 seconds
before the gas valve is energized. If the
burner does not light (flame is not
established within 7 seconds), this control
will lock out gas flow until the control is reset. If flame
signal is lost during burner operation, the control will
allow one retry for ignition.
HIGH PRESSURE REGULATOR (HPR)
The HPR option is required when the
gas supply pressure exceeds the
nameplate rating for the heater. Unless
otherwise specified, the HPR assembly
is also furnished with a high gas
pressure manual shut-off valve and a
tap for measuring the upstream gas pressure. The HPR
must be a positive lock-up type regulator which must be
vented to outdoors. It is sized according to the gas
supply pressure and the capacity requirements of the
heater.
IGNITER (IGN)
The hot surface igniter is the ignition source
for lighting the gas in the burner. It is made
of silicon carbide which is very fragile. Care
should be used in handling. It operates on
24 Volts and the current ranges from 1.3 to 1.7 amps. It
will reach temperatures in excess of 2400˚F during the
ignition trial.
MODULATING VALVE (MV)
The MV responds to a 4 to 24 Volt DC signal
from the amplifier to modulate the flow of
gas to the burner. The low fire adjusting
screw is located on the side of the valve
under the dust cover.
HEATER COMPONENTS
AIRFLOW SWITCH (AF)
The airflow switch senses the pressure
drop across the burner. It is factory set
and not adjustable. It is designed to
prevent burner operation if the airflow
drops significantly below the minimum
design airflow of the heater.
