31
Every second during a run, the
personal
DataRAM serial port will output a sixteen-
character code. It consists of two brackets with 14 hexadecimal digits between them,
representing sum check (2 digits), sensed concentration (8 digits), and calibration
factor (%, 4 digits). The concentration in µg/m
3
is obtained by multiplying the
sensed concentration times the calibration factor and dividing by 100.
10.0
ANALOG SIGNAL OUTPUT
10.1
Analog Output Description
The
personal
DataRAM incorporates the capability to provide both a voltage and a
current signal output directly proportional to the sensed concentration of airborne
particulates. Both these analog signal outputs are concurrently available. These
outputs are provided, principally, for fixed-point applications with hard-wired
installations, such as for continuous HVAC monitoring and control.
The particulate concentration range corresponding to the output voltage and current
ranges (0 to 5 V and 4 to 20 mA) can be user selected (via a PC). The most sensitive
range available is 0 to 0.100 mg/m
3
, and the least sensitive range is 0 to 400 mg/m
3
.
For example, if the user selects the analog output range of 0 to 0.400 mg/m
3
then the
analog output signal levels, at a concentration of 0.200 mg/m
3
, would be 2.5 V and
12 mA.
Selection of the concentration range of the analog output must be performed on the
PC. This range is independent of the digital display, data logging and real-time
digital output range which are controlled automatically (auto-ranging).
Enabling the analog output increases the current consumption from the power source
(battery or power supply) of the
personal
DataRAM by typically 5 mA when no load
is connected to the analog signal current output. If such a load is connected then the
current consumption of the
personal
DataRAM further increases by the magnitude of
the output signal current (up to a maximum increment of 20 mA). Therefore, when
not using the analog output, it is advisable to disable that output (see Section 8.2) in
order to minimize power consumption (this is important only when powering the
personal
DataRAM from a battery source).
10.2
Analog Output Connection
The
personal
DataRAM is provided with a cable (model
p
DR-ANC) which has a 6-
contact plug at one end and flying leads at the other. There are 4 leads for the analog
and alarm outputs. The additional two contacts of the connector are used only for
digital communication with a PC, for which a separate cable (model
p
DR-DCC) is
provided.
Counting from top to bottom on the
personal
DataRAM connector receptacle, contact
#1 is the positive 4 – 20 mA analog output, contact #2 is the alarm output, contact #5
