59
Fig. 90 — Signal Conditioner SC30
INDUCER FAN SPEED CONTROL
For an example of an inducer fan speed control, see Fig. 91.
Fig. 91 — Inducer Fan Speed Control
TIMER RELAY CONTROL (TR1)
See Fig. 92. The timer function is as follows:
1. The TR1 receives a 24 vac signal (terminal 7), normally from
the ignition control MV gas valve output or the thermostat
circuit (see Note 1). Upon receiving the signal the TR1 begins
multiple tasks. It starts Timer No. 1, lights the SR LED,
places the 2-stage gas valve in either the high or low pressure
stage (terminal 9), places the inducer in either the high or low
speed (terminal 12, 13) and powers the Series 3 or SC30 (ter
-
minal 10).
The TR1 maintains this mode throughout Timer No. 1’s dura
-
tion, regardless of the temperature controller input (it is ignor
-
ing terminal 6). The initial gas valve stage, initial inducer
stage, and length of time are customer specified and pro
-
grammed into the TR1. Specifying these factors can elimi
-
nate problems associated with lighting the burner at an
undesirable input and condensation occurring at start-up.
(When using the Maxitrol modulating system, the SC30 and
Series 3 controllers output a constant voltage to the modulat
-
ing gas valve thereby fixing an approximate input rate during
the set time after power up. The time, which is often set equal
to the TR1 Timer No.1 duration, and the output voltage are
fixed or adjustable. See SC30 and Series 3 literature.)
2. When Timer No. 1 expires, the TR1 defaults the gas valve
and inducer to low pressure/speed mode and hands control of
the required mode, high or low, to the temperature control
system. The MR LED lights and the SR LED goes out. The
terminal 6 input signal (0 to 24 VAC) now determines if the
gas valve and inducer will remain in the low pressure/speed
mode or switch over to the high pressure/speed mode.
When the terminal 6 input signals the TR1 to switch to the
high output mode, it starts Timer No. 2. Timer No. 2 is pro
-
grammed to a customer specified time and is used to buffer
the low to high switch point. When Timer No. 2 expires, the
system switches from low output mode to high output mode
(see Note 2).
3. The FR LED lights when the inducer operates in high speed.
4. The CR LED lights when the gas valve operates in the high
pressure stage.
5. Use terminal 8 to accept a “made” inducer high air flow
switch (HAFS) signal. If the 24 VAC signal is not received,
the TR1 keeps the gas valve in the low pressure stage, regard
-
less of the terminal 6 input signal.
NOTE 1: Timer No. 1 resets each time power is removed from ter
-
minal 7. Tip: By reseting each time power is removed from termi
-
nal 7, the fan purge setting and time do not need to be considered,
and the start time duration will be the same, even after failed igni
-
tion attempt(s).
NOTE 2: Immediate low mode to high mode changeover after
Timer #1 expiration, or upon receiving required terminal 6 signal,
can be accomplished by specifying Timer No. 2 to zero seconds.
IMPORTANT: To avoid internal damage to the SC30 Signal
Conditioner the transformer’s secondary must not be grounded
in any portion of the circuit external to the SC30 Signal Condi
-
tioner. If existing transformer is grounded, a separate isolated
transformer must be used.
SC30
R18
R22
a62-582
WARNING
To avoid internal damage to the TR1, Transformer No. 2 (see
Fig. 93) secondary must not be grounded in any portion of the
circuit external to the A1093/SC30. A separate, independent
transformer is recommended.
