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Oxygen applications monitoring both increasing AND decreasing oxygen
concentration must have the INHIBIT level programmed below 4 mA. When the input
signal reaches the inhibit level, the relays are turned off. 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.
Current Loop Outputs
Each channel provides a 2 wire isolated current loop output which follows the current loop input, except during the
following conditions:
Alarm inhibit:
Current loop output goes to programmed inhibit level.
Channel Off:
Current loop output goes to programmed inhibit level.
Input Under range
(below 4mA): Current loop output follows the current loop input until it reaches the
programmed fault level. At that stage, the value remains at the fault level no matter how
far down the current input goes.
Internal Faults:
Current loop output goes to the programmed fault mA level.
Alarm and Relay Operation
When an increasing or decreasing toxic, explosive, or oxygen deficient gas condition or flame is detected, the
QuadScan II provides the means to alert to this potential hazard. An increasing gas concentration is normally
associated with toxic or combustible gas atmospheres, while decreasing concentrations are associated with oxygen
deficient atmospheres.
An alarm due to an increasing concentration is activated (changes state) when the displayed digital indication is at or
above the set point and is inactive when the digital indication is at or below the reset point. Flame detectors provided
by Scott Health & Safety provide an increased output analog signal when a flame is detected.
An alarm due to a decreasing concentration is activated (changes state) when the digital indication is at or below the
set point and inactive when the digital indication is at or above the reset point.
Protection is provided by the activation (change of state) of alarm relays, which can be used to activate protective
devices such as deluge systems, shut down systems, horns, beacons, etc. Two common relays (warn and alarm)
each with 5A SPDT contacts provide this interface. An optional relay assembly provides eight additional relays that
can be configured for any channel.
Set Point - A programmed numerical value that is compared to the actual gas concentration or percentage of full
scale. When the concentration is equal to this numerical value, the associated relay activates (changes state)
immediately. (See Set Delay).
Set Delay (Off Time) - A delayed relay activation can be programmed for a specific time delay until a constant gas
concentration is established at or above the set point (toxic/ combustible or flame applications) or at or below the set
point (oxygen deficient applications) for that specific programmed period of time.
Summary of Contents for QuadScan II 7400
Page 10: ...5 of 116 Quick Start Programming Menu Tree...
Page 20: ...15 of 116 Figure 5 Mounting Dimensions of Model 7400...
Page 24: ...19 of 116 Figure 9 Battery Backup P N 096 0719 Outline Interconnection Wiring...
Page 60: ...55 of 116 Figure 13 Interconnect Wiring Between 7400 Remote Relay Assembly...