32
is the common ground (return for all signals), and contact #6 is the positive 0 – 5 V
analog output.
For the 0 – 5 V output signal, the externally connected load must have an impedance
of more than 200 kilo-ohms. For the 4 – 20 mA output signal, the externally
connected load must have an impedance of less than 200 ohms when powering the
personal
DataRAM with a battery, or less than 300 ohms when using the its AC
supply.
Since both voltage and current outputs are present at the same time, both can be used
concurrently, if so required.
The accuracy of the analog output signals is better than 1% of the reading with
respect to the digital reading.
11.0 ALARM
11.1
Alarm Description and Operation
The
personal
DataRAM alarm function is provided both as an audible signal as well
as an electrical output. The audible alarm consists of a series of beeps generated by
an on-board piezo-transducer. The electrical output, available at the digital
communications port, consists of a 1 Hz square wave signal which can be used to
trigger/activate other equipment through an appropriate interface (consult with the
factory).
The alarm function can be enabled/disabled by the user through the
personal
DataRAM keyboard (see Section 8.2). Setting of the alarm level must be
performed on the PC (see Section 9.0).
The alarm is triggered whenever the preset alarm level is exceeded based either on:
a) the displayed real-time concentration, if ALARM: INSTANT was selected (see
Section 8.2), or b) a 15-minute running average concentration, if ALARM: STEL
was selected. When the concentration falls below that level the alarm condition
stops. While the alarm is on the user can stop it (i.e. silence the alarm) by pressing
any key of the
personal
DataRAM. If the concentration continues to exceed the set
alarm level after 10 seconds, however, the alarm restarts.
11.2 Alarm
Output
A pulsed voltage output is available on the
personal
DataRAM in synchronism with
the audible signal. This signal consists of a 1 Hz square wave with an amplitude
level of 5 V pp. An externally connected load should have an impedance of no less
than 100 kilo-ohms. This alarm output signal is available at pins 2 and 5 (counting
from top to bottom) of the 6-contact output/communications port on the side of the
personal
DataRAM (see Figure 5 or 6).
