L60iF Issue 9 November 2018 17
This is the first of five breakpoint values that define the linearising characteristic of the sampler. Linearisation
is necessary because the input signal to the microprocessor is proportional to the pressure drop across the
orifice in the air flow path. As the true flow is proportional to the square root of the pressure drop,
linearisation is used effectively to take the square root of the input signal.
To see the other four Breakpoints, press the (o
) key four times. Typical readings -
48 l/min ADC 0181.2 53 l/min ADC 0204.5 58 l/min ADC 0224.6 63 l/min ADC 0253.8
If these values are plotted they should lie on a shallow curve.
At any time while viewing breakpoints, pressing (
) moves the display to
This is the first of six displays related to temperature calibration. This is used to compensate for potential
flow reading errors during the period that the pump is warming up, usually the first 20 to 30 minutes of
running. Without compensation, short samples (e.g. 10 minutes) will be recorded inaccurately. (In an 8-hour
run the error would be negligible even without compensation.)
As indicated on screen, pressing key (
) displays the next data, pressing (
) reverts to the previous data.
Pressing (
) at any time prepares the instrument for a calibration check.
It can be seen from the above typical figures that there is a difference of nearly 4 l/min between true and
L60iF measured flow when the pump is cold, and only a small residual difference of 0.3 l/min when the pump
is hot. It is this difference that the temperature Compensation addresses, adjusting the correction depending
on the pump temperature, which is continuously monitored by a sensor. These data are discussed more fully
later.
Cold pump temp
Cold measured flow
Cold true flow
Hot measured flow
Hot true flow
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