L60iF Issue 9 November 2018
9
4. Technical Description
The L60iF is a large volume air sampler with a nominal sampling rate of 60 litres per minute. It uses a
standard Munro Instruments Pump and Motor unit to draw air through a 60mm open face filter holder.
There is an orifice assembly in the airline between the filter and the pump. The pressure drop across this
assembly is accurately measured by a pressure sensor which produces a 10 bit digital output proportional to
the pressure drop for direct connection to the control PCB. Airflow is proportional to the square root of
pressure drop, and a linearisation curve with four break points is used to perform the necessary square root
function. This output is scaled and then used to display and store the airflow rate. Volume sampled is
calculated by integrating the flow rate over one second intervals. Thus if the flow rate drifts, the volume
measurement remains accurate.
All selection of test routines is carried out using the vacuum luminescent display in conjunction with the four
directional push buttons. Software routines configure the display and buttons in either an Operating or a
Supervisory mode. The memory that stores the chosen routines etc. is battery backed, the battery having a
nominal life of 10 years. There is also a Calibration mode, which is entered in a similar manner to the
Supervisory mode, by holding down selected pushbuttons while powering up the unit. The user can calibrate
the L60iF against a traceable flow gauge at any time.
A Diagnostic menu gives access to stored parameters and data about the history of the sampler. (First
powered date, total run time, calibration date etc.)
Total volume is calculated as the time integral of (Flow
u
Sampling period). The accuracy of time
measurement within the microprocessor is so high that volume measurement is effectively as accurate as the
flow measurement.
The interior of the unit is cooled by a fan. The air inlet is filtered to minimize build-up of dust etc. within the
case. The filter support also acts as an EMC screen. The air filter should be replaced at regular intervals. Spare
packs of five filters are available from Munro Instruments.
Mains and other filtering are included to ensure compliance with current LV and EMC European Directives.