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VOC Operation
(Ver. 2 firmware) 20-11-17
1.
The circuit is designed to work with TGS822 or TGS 2620
2.
The input supply voltage is 12VDC
—
30VDC. A bridge rectifier is used to protect against reverse
polarity, and a bypass shunt (LK3) will allow for common ground (if preferred). The VOC can also be
powered by an AC source (with LK3 open).
Note: Whether powered by DC or AC, it is extremely important that the rectified voltage (measured
across VS l) does not exceed 30 Volts.
3.
A Green LED indicates power ON. When the VOC is powered, the LED will flash for 5
minutes with all other activity disabled. The flashing LED indicates that the sensor is
stabilizing.
4.
Two relays, Relay Lo (K2/JP5) and Relay Hi (Kl/JP4) are activated at pre-set trigger points.
a.
Relay Lo trigger ON point
—
2.5 V (measured at TPI relative to GND)
b.
Relay Hi trigger ON point
—
3.5 V (measured at TPI relative to GND)
c.
Relays turn OFF at 10% below their respective trigger points.
d.
When Relay Lo or Relay Hi turns ON, they will stay on for a minimum of 1 minute.
e.
While the Green LED is flashing during power on, the relays are OFF.
5.
A multi-turn potentiometer (P l) allows the user to vary the amplification of the sensor
signal in order that the alarm trigger (Relay Hi) occurs at the desired concentration for the
specific Volatile Organic Compound being sensed.
Note: The value ofR8 can be changed to vary the range of the sensor. A lower value decreases
sensitivity (increases range) and a higher value increases sensitivity (decreases range).
6.
2 red LEDs, Led Lo (D3) and Led Hi (D2) are used to indicate the relay condition.
a.
Led Lo is ON when Relay Lo is ON and OFF when Relay Lo goes OFF.
b.
The same operation occurs for Led Hi and Relay Hi.
c.
Led Lo and Led Hi will flash when the sensor level rises to within 5% of their
respective trigger points. This provides an early warning that the sensor level is
approaching the trigger point.
7.
A Buzzer will activate when Relay Hi turns ON and will shut off when Relay Hi turns OFF. The
Buzzer can be silenced using an external kill switch wired to LKI or by pressing the onboard
pushbutton switch.
8.
For testing and calibration purposes, the 1-minute Relay-ON timers and/or the 5-minute Power-ON
warmup time can be bypassed using the on-board pushbutton switch.
a.
To bypass the 1-minute Relay-ON timers and the 5-minute Power-ON warmup time,
hold down the pushbutton switch first and then apply power to the VOC. Hold the
button down for approximately 5 seconds until the green LED stops flashing.
b.
To bypass only the 5-minute Power-ON warmup time, hold down the pushbutton switch
after applying power to the VOC. Hold the button down for approximately 5 seconds until
the green LED stops flashing.
