BAM 1020-9800 Manual Rev W.docx
Page 74
8
EXTERNAL DATA LOGGER INTERFACE SYSTEM
This section describes the configuration of the BAM 1020 to work with a separate, external
data logger. The BAM 1020 provides an analog concentration output voltage along with a
clock synchronization input feature which allows unit to function with many analog data
loggers. The BAM 1020 digital data outputs can also be collected with digital data loggers or
automatic digital data acquisition systems. In any case, the BAM 1020 internal digital data
logging system still stores the complete data array, which can be collected periodically.
This section describes the BAM 1020 configurations required for external data loggers.
Consult your data logger documentation for the specific setup requirements for your model.
Met One Instruments can also supply technical bulletins describing sample setup
programming for several of the more popular types of data logger.
8.1 Analog Concentration Output Signal
The BAM 1020 analog output type is selectable between voltage output (0-1 or 0-10 volt DC)
or isolated current output (4-20 or 0-16 mA). The rear panel dipswitches are used to select
the desired output as shown in the table below. The 1-volt voltage output is almost
exclusively used for analog data logging applications.
SWITCH
ON
OFF
SW1
0-10 vdc
0-1 vdc
SW2
4-20mA
0-16mA
SW3
Not used
Not used
SW4
Not used
Not used
Important Note:
The scale of the output voltage of the BAM 1020 is determined by the
RANGE and OFFSET setting. See Section 6.2. In most applications where the OFFSET is
set to -0.015, and the RANGE is set to 1.000 mg, the BAM 1020 analog output will be scaled
as
0.000v to 1.000v equals -0.015 mg to 0.985 mg.
It is critical that your analog data logger
input is programmed to scale this voltage correctly, or a significant data offset mistake will
occur! The BAM digital data should be periodically compared to the analog logger data to
ensure correct logger scaling. In addition, the BAM output voltage DAC should be tested as
described in Section 7.12 to ensure that the actual voltage output of the BAM matches the
expected voltage.
Analog Error Encoding:
The analog output is the only voltage channel available between
the BAM 1020 and the data logger, so any errors generated by the BAM are reported using
the same voltage signal. The BAM 1020 will set the analog output to its full-scale reading
whenever a critical error prevents a valid concentration from being measured. It can
optionally set the voltage to full-scale in response to other non-critical alarms as described in
section 6.5. The external data logger should be programmed to recognize a full-scale reading
as an error, and not a valid concentration. This method is used because it is rare for an actual
concentration reading to exceed the range of the BAM 1020, and if it does, it should be
reported as an invalid data point anyway. The digital data values stored in the BAM are
always unaffected and available, if the alarm was non-critical and did not prevent the hourly
concentration measurement from occurring.
