Analytical Industries GPR-1600 Series Trace PPB Oxygen Analyzer - Manual (Page 20)

Advanced Instruments Inc.
20
Alarms
The analyzer is configured with two user adjustable threshold type alarm relays that can be configured in the field from the
ALARM option on the MAIN MENU as follows:
¾ Establish independent set points
¾ Either Hi or Lo
¾ Either On or Off (enabled or disabled)
¾ Both temporarily defeated using a user entered ‘timeout’ period (normally minutes)
The alarm set point represents a value. When the oxygen reading exceeds (high alarm) or falls below (low alarm) the alarm set
point, the relay is activated and the LCD displays the alarm condition.
When activated the alarms trigger SPDT Form C non-latching relays @ 5A, 30VDC or 240VAC resistive. To prevent chattering of
the relays, a 2% hysteresis is added to the alarm set point. This means that the alarm will remain active until the oxygen
reading has fallen 2% below the alarm set point (high alarm) or risen 2% above the alarm set point (low alarm) after the alarm
was activated. The timeout feature is useful while replacing the oxygen sensor or during calibration when the oxygen reading
might well rise above the alarm set point and trigger a false alarm.
Note: When making connections the user must decide whether to configure/connect Alarm 1 and Alarm 2 in failsafe mode
(Normally Open – NO – where the alarm relay de-energizes and closes in an alarm condition) or non-failsafe mode (Normally
Closed – NC – where alarm relay energizes and opens in an alarm condition).
Power Failure Alarm
A dry contact rated at 30VDC @ 1A is provided as a power failure alarm that activates when power supplied to the analyzer’s
circuits is unacceptable. The contact is normally closed but opens when the power to the analyzer is switched off or interrupted
and cannot be disabled.
4-20mA Signal Output
The analyzer provides a 4-20mA full scale fully isolated ground signals for external recording devices. The integral IC on the
main PCB provides 4-20mA fully isolated signals for output and range ID. The 4-20mA current output is obtained by connecting
the current measuring device between the positive and negative terminals labeled OUTPUT 4-20mA. To check the signal output
of the 4-20mA E/I integrated circuit connect an ammeter as the measuring device and confirm the output is within +0.1mA of
4mA. A finer adjustment of the zero offset of the 4-20mA converter can be provided by a potentiometer mounted on the main
PCB Assembly. Consult factory for instructions
Range ID
For range ID the output of 4mA, 8mA, 12mA, 16mA, 20mA correspond to the most sensitive to least sensitive analysis range.
The standard 4-20mA output used for range indentification, as described below, can be replaced by eliminating the alarms
feature and using the relay contacts associated with the alarms to provide a single common and four (4) normally open relay
contacts that close when the related range is active. The dry contacts are rated at 30VDC @ 1A and powering them is optional
as some PLCs can distinguish contact closure via continuity check.
Caution:
The integral 4-20mA converters are internally powered and do not require external power. DO NOT supply any
voltage to any of the two terminals of the 4-20mA converter.