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Aeroqual Series 900 User Guide
2.2.4. 4-20mA output scale
The 4-20mA output scale sets the gas concentration scale. Each sensor head type has a default
setting but the user can modify this by clicking the user define button and entering the required value
that corresponds to 20mA.
2.2.5. Upload
Clicking this button uploads the settings to the instrument.
2.2.6. Download
Clicking this button downloads the settings from the instrument. Use this function to check the settings
are correct.
3. Operation
3.1. Description of Outputs
DIAG
This output is designed to enable detection of sensor faults. This is normally floating but is set to GND
when the sensor fails. Thus it can be considered a "switch" which is closed when the sensor fails. This
can be used to activate an alarm or relay and can also be monitored with a PLC. The output is an
open collector current sink. The maximum rating of the transistor output is 24VDC at 150mA.
LoALM
This is set to GND when low alarm is activated. It is floating at other times. Use the Configuration
Program to set the Low alarm set point. The output can be used to drive an alarm relay or similar. The
alarm can be set to trigger above or below the set point using the configuration software. The output
is an open collector current sink. The maximum rating of the transistor output is 24VDC at 150mA. If a
relay coil is connected or any other inductive load to the transistor outputs, a back EMF suppression
diode must be fitted across the load.
HiALM
This is set to GND when high alarm is activated. It is floating at other times. Use the Configuration
Program to set the Hi alarm set point. The output can be used to drive an alarm relay or similar. The
output is an open collector current sink. The maximum rating of the transistor output is 24VDC at
150mA. If a relay coil is connected or any other inductive load to the transistor outputs, a back EMF
suppression diode must be fitted across the load.
CNTRL
This is set to GND when the gas concentration is rising in the range from below the Control low set
point to the Control high set point at which stage, it is set to floating. It remains floating until the
concentration falls below the Control low set point at which point, it is reset to ground. Use the
Configuration Program to set the Control set points. This output can be used to control, for example, a
gas generator or vent in a process operation. The output is an open collector current sink. The
maximum rating of the transistor output is 24VDC at 150mA. If a relay coil is connected or any other
inductive load to the transistor outputs, a back EMF suppression diode must be fitted across the load.
STBY
STBY is a hardware toggle switch. If it is briefly pulsed (about 50ms) to GND it puts the sensor head
into Standby mode and the S930 into Sleep mode. If pulsed again to GND it will return to normal
operation. This can be used to protect the sensor during process room cleaning and/or to reduce
power and extend sensor life when the sensor is not needed.