Scott QuadScan II 7400, Operation & Maintenance Manual, Page: 26 / 121

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Channel Status
The channel status essentially provides a summary of the health of each active channel. Four LEDs are used,
one for each of the 4 channels. Each LED provides 3 functions:
Channel OK - Green
Channel in Fail - Flashing yellow, (solid yellow when reset button is pressed)
Channel Inhibited - Flashing yellow/green
Alarm Status
Each channel has 2 LEDs, warn (yellow), for low alarm status and alarm (red)
for high alarm status. The operation of these LEDs are controlled by the display
indication (gas concentration ) and the alarm settings(set points). During normal
operation these LEDs are not illuminated, when an alarm condition is detected,
its respective LED will illuminate in a flashing mode.
The warn LED can be illuminated by itself or both the warn and alarm LEDs can
be illuminated at the same time, depending on the level of the gas concentration
detected. The LEDs will remain flashing until the alarm condition has passed or
until the alarm reset pushbutton is pressed. If the alarm condition is still present after the alarm reset has been
pressed, the LEDs will remain illuminated but not flashing. If the alarm is programmed as latching, the LED will
extinguish only after pressing the alarm reset when alarm conditions are not present (above or below the reset
point). Warn represents the first stage of alarm while alarm represents a more serious event.
Current Loops
During factory calibration, each current loop is exposed to a precise 4.00mA and 20.00mA input signal which the CPU
stores as digital values in EEPROM. These values are then used to determine the unknown input current during
normal operation. The computed mA input value is then used for computing the digital display, where 4mA is
equivalent to 0.00, and 20.00mA is equivalent to the programmed full-scale display.
WARNING: In normal operation the 4-20mA input current loop is checked for a signal that falls down to or below
the programmable fault level. The factory default level is 3.5mA but can be programmed as low as 1.0mA.
Applications such as oxygen deficiency monitoring must have the FAULT level programmed below 4 mA.
When the input signal reaches the fault level, the relays are turned off after the alarm reset button is pressed.
Therefore setting the alarm level below 4mA (0.0% v/v O2) will prevent the 7400 from shutting off the warn and
alarm relays accidentally.