Selection Of The Orifice; Installation Of The Orifice - Merck APC SmartTouch Operation Manual

NOTe:
The correct orifice must be selected for the input pressure and output flow rate, or the particle count accuracy will be affected.
The CGA may be mounted to a wall using the included
bracket, or it may simply be connected to the pressure line
if the line can support the weight.
CGA Installation
To sample a compressed gas line you must first select and install the correct orifice to the particle counter. Then, attach the device to
the pressure line.

selection of the Orifice

The orifice in the CGA drops the pressure to atmospheric, while also limiting the flow rate. When an orifice is used in this manner,
the flow rate from the orifice is pressure dependent. In the CGA, the correct orifice must be used to keep the flow rate in a desired
range for a given input pressure.
If the flow rate from the orifice is less than the flow rate of the particle counter, then the counter will pull in air through the
vent port in addition to the air that is sampled from the pressure line. This will lead to an incorrect particle count in the
pressure line. Conversely, if the flow rate from the orifice is too high, then the isokinetic condition is not met in the CGA, and
the particle counts could be biased higher, especially for the larger size channels.
1. Make sure the flow rate your orifice set was designed for matches your instrument flow rate.
100 lpm for APC M3,
50 lpm for APC M3,
1.0 cfm for APC Portable,
0.1 cfm for all APC Handheld,
0.1 cfm for APC ErgoTouch (Pro), article no. 1.44180.0001
2. Find the input pressure in the line to be sampled.
3. Match the correct orifice number to use following the pressure range indications given in the orifice set box.
Install that orifice in the CGA inlet. (Section 5.2 )
NOTe:
If the pressure fluctuates from one orifice range to another, use the orifice for the lower pressure. This will keep the flow rate
high enough to ensure that the excess gas exits the device from the vent port and that air is not taken in through the vent.

Installation of the Orifice

All threads from the pressure line to the orifice should be sealed. This will prevent leaks into the cleanroom that could cause particu-
late contamination. It is also recommended to seal the threads in the inlet, outlet, and vent port of the CGA. This will help to ensure
that no air is drawn in from the cleanroom through the CGA and into the particle counter.
The inlet port, outlet port and vent port all have 1/8 inch NPT threads. These threads are tapered, so that the more that a fitting is
screwed in, the tighter the fit gets between the two parts being connected. In theory, to provide a complete seal between the mating
parts, all that needs to be done is to tighten the fittings more. However, in practice thread sealing tape or compound is used to help
seal the threads.
article no. 1.44166.0001
article no. 1.44168.0001
article no. 1.44170.0001
article no. 1.44172.0001
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