6 Operating Instructions
19
Air Supply Local Operation
Start up the system following chapter 6.1 and heat up the evaporation tube.
Start the instrumentation connected to the testo ASET15-1 therewith the measuring gas
flow desired for the pending measurements is drawn from the measuring gas output 13).
Set the secondary dilution air supply potentiometer 8) on its mechanical zero position to
set the secondary dilution factor to 1.0 which actually means no secondary dilution.
Switch on the secondary dilution air supply 4). The secondary dilution air supply LED 5)
lights red first and turns to green after a few seconds to indicate the secondary air supply
pump working properly.
If the connected sensors draw less than 1.2
l/min, the sufficient excess measuring gas
flow LED 10) lights green as soon as the flows are stable. The testo MD19-3E raw gas
pump can be switched on and the measurements can start if the primary diluter is ready
and no secondary dilution is required e.g. due to too high concentrations in the
measuring gas or for reducing thermophoretic losses according to appendix A.3.
If a higher amout of measuring gas is drawn, the low measuring gas flow LED 11) lights
red indicating that the excess gas flow is below 0.3
l/min or could even be negative which
would mean air was sucked backwards through the excess gas port 12) and mixed in an
undefined way with the measuring gas.
In this case enhance the secondary dilution flow Q
AS
by adjusting the secondary dilution
air supply potentiometer 8) until the light signal changes to the green flow OK LED 10).
Increase the flow 0.1...0.3 potentiometer units over the limit where the green LED starts
to light to find the ideal measuring gas flow setting.
The secondary dilution can be used to increase the total dilution factor as well as to
reduce thermophoretic losses. If it is set as high as more measuring gas is conditioned
and provided than needed by the connected sensor(s), a certain back pressure can arise
in the measuring gas stream due to the filter in the excess gas tube. Therefore the high
excess gas LED 9) lights yellow if more than 1.5
l/min pass the excess gas port. This
back pressure can reach up to 16
mbar at maximum secondary dilution and zero
measuring gas flow.
The total particle concentration reduction factor PCRF is the product of the primary dilution factor
set at the testo MD19-3E, the secondary dilution factor set at the testo ASET15-1 and the inverse
of one minus the fraction which is not lost due to thermophoretic losses.
Example: testo MD19-3E primary dilution factor:
30
testo ASET15-1 secondary dilution factor:
3
thermophoretic loss (see appendix A.3):
10%
=
0.1
PCRF
=
30 ⋅ 3 ⋅
1
1−0.1
=
30⋅3⋅1
0.9
=
90
0.9
=
100
Note: When switching OFF the secondary dilution air supply switch 4), wait at least 10 seconds
before restarting in order to avoid short peak flows in the order of 20
l/min on the measuring gas
output 13)
6.4.
Remote Operation
Remote communication with testo ASET15-1 is possible with analog and digital inputs and
outputs at the digital/analog interface 27) at the rear side of the device. The signals on this
connector are described in chapter 7.2.
Besides the remote interface of the integrated testo MD19-3E Rotating Disk Diluter is connected
to the corresponding plug 26) at the rear side of the testo ASET15-1 case. The function and pin
assignment of this connector are the same as the ones of the connector at the rear side of the
testo MD19-3E stand alone case which are described in the testo MD19-3E user manual.
