Hach ORBISPHERE ATEX 366 Série Manuel D'utilisation Simplifié page 9

3.6.2 Analog output signal
The analog output signal, representing the measured gas concentration, is available from the
instrument in the ranges from 0 to 20 mA, or in the range from 4 to 20 mA. In addition, the model
3662EX has a second analog output of 0 to 2 Volts. Depending on the instrument model, separate
output connections are available for the "safe" area and for the "hazardous" area.
Scale these outputs between two custom concentration limits. If the lower of these limits is
represented by AL, and the upper one by AH, the relation between the output current I (or voltage V)
and the gas concentration C is as follows:
0 – 20 mA
4 – 20 mA
0 – 2 Volts
The analog output saturates at 20 mA (or 2 Volts), or is blocked at 0/4 mA (or 0 Volts) under various
conditions, as summarized below:
Analog output
0/4 mA (or 0 Volts)
0/4 mA (or 0 Volts) < signal < 20 mA
20 mA (or 2 Volts)
3.6.3 Alarm relay output (3660EX only)
There are three separate alarm relay connections on the instrument's output card (NO and NC), for
each alarm limit relay (High and Low), and system (SYST) alarm. The following table lists the
possible alarm conditions.
Conditions
Instrument power
switch off
No alarm:
Low Limit < measured
gas < High Limit
Low alarm:
measured gas < Low
Limit
High alarm:
measured gas > High
Limit
System test
Sensor not connected
Thermal cut off
* Low NC, High NC, Low NO, High NO, and Com identify the alarm relay connections on the instrument's output
card.
Note: The system alarm is turned on when the following situations are met:
Instrument off - Alarm high - Alarm low - Sensor out - Thermal cut off
C = AL + (AH - AL) * I/20
C = AL + (AH - AL) * (I - 4)/16
C = AL + (AH - AL) * V/2
Thermal cutoff or below analog output low limit (AL)
Normal operating condition
Over range, above analog output high limit (AH), or sensor disconnected
Low alarm High alarm
NC to Com* NC to Com*
closed closed
open open
closed open
open closed
closed open
Explanation
Low alarm High alarm
NO to Com* NO to Com*
open open
closed closed
open closed
closed open
open closed
Alarm syst Alarm syst
NC to Com* NO to Com*
closed open
open closed
open closed
open closed
closed open
closed open
closed open
English 9