Oxigraf O2iM NEMA 4X Oxygen Analyzer
February 13, 2007 08-0427-B0, Manual, O2iM.doc Page 10
3.1.5 4 – 20 mA Analog Output
A measure of percent oxygen is available at the 4 – 20 mA analog output on TB2. The oxygen
concentration at 4 mA and 20 mA is a programmable parameter that can be set via the keypad. The 4
to 20 mA current output is a non-isolated active current source referenced to the TB2 Gnd terminal.
The maximum output voltage is equal to the O2iM DC supply voltage minus 2 volts. For example, if
the supply voltage is 24 volts then the maximum output voltage at 20 mA is 22 volts.
Note: The 4 – 20 mA signal ground is connected to the sensor chassis ground and DC power
supply ground.
3.1.6 Relay Contacts
The standard unit has a single alarm relay as described in the next section. The other relays described
below are on the optional 5-relay board.
Access to five SPDT relays (P&B PE series) is provided at the TB3 and TB4 terminal strips. For
DC resistive loads the relay contacts are rated for 5 amps at 30 volts open circuit, decreasing to 0.25
amps at 300 volts open circuit. For AC resistive loads the contacts are rated for 5 amps at 250 VAC
open circuit.
The limit A and limit B relays can be programmed to activate on conditions of high O2, low O2, or
both. In addition, each limit relay can be configured to latch or flash on an alarm condition. A
latched limit detector is reset by pressing any key, if the limit condition that set the latch is no longer
true. Limit relay activation can delayed from the assertion of the limit condition by setting the Alarm
Delay parameter to the delay time. Transient limit or warning conditions shorter than the delay time
will not result in a limit alarm.
The WARNING relay activates on detection of a system problem such as low flow, high pressure, or
self-test failure. The SYS OK relay is turned on when the analyzer has warmed up and passed its
internal self-test process. The optional ALARM relay activates under various programmable
conditions of limit and warning conditions. It normally drives the horn and strobe but may be used
as an external system alarm contact.
When the multipoint sampler is installed the Channel Relay Mode may be enabled. In this case the
LIMIT A, LIMIT B, WARNING, and SYS OK relays are reassigned as individual channel alarms.
A specific relay will activate only if an alarm condition is true for that channel. The flash and latch
setup options still apply to the limit detectors and will drive the channel relays appropriately.
A global failsafe mode may also be programmed that inverts the relay drive for an alarm or warning
condition. The normal state of the LIMIT A, LIMIT B, and WARNING relays will be ON, and the
specific relay will turn off when the alarm or warning condition becomes true. In Channel Relay
Mode the failsafe mode applies to the four channel alarm relays. In both modes an active warning
condition will turn off the limit or channel alarm relays irrespective of the limit detector status.
The relay logic can also be configured in Exclusive Mode, which activates only the highest priority
alarm or status relay. This mode is intended for driving a remote four-light indicator where it is
necessary to have only one light illuminated at a time. The priority ranking, from low to high, is SYS
OK, WARNING, LIMIT B, and LIMIT A.
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General