VICI 340 Dynacalibrator - Manual (Page 15)

11
Bypass Loops
Only those Dynacalibrators with internal pumps are equipped with fittings for
bypass loops in either or both the carrier and dilution streams (input configura-
tions -3X, -4X and -5X). The fittings – labeled CARRIER OUTLET, CARRIER INLET,
DILUTION OUTLET, and DILUTION INLET – are downstream from the pump, so
the loops must be completed in order for the internal pump to be used . The
purpose of the loops is to expedite the installation of external filters, scrubbers,
dehydrators, etc. into the two internal streams before each is mixed with the
trace gas. All plumbing should be as short as possible, and the devices should
not restrict the flow in either stream below their normal operating rates. If a
separate gas supply is connected to either inlet, the input pressure should be
between 5 and 16 psig, and the companion outlet should be capped.
If external devices are not required, then the outlet ports must be directly
plumbed to their companion inlet ports.
Stream, Span, and Zero Outlets
Since the Model 340 can supply zero air as well as span gas from its primary outlet,
that outlet is labeled STREAM OUTLET. The stream outlet may be either perma-
nently plumbed to the calibrate input port of an analyzer or temporarily connected
to its sample input for calibration, depending on the capabilities of the analyzer.
NOTE: The span outlet port should be directly connected
to the analyzer input with a minimum length of tubing.
Altering the output stream in any manner may affect the
concentration of calibration gas in the stream.
The zero outlet port provides a scrubbed supply of ambient air for a zero point
calibration. Since it is not pressurized, the zero outlet requires suction from the
analyzer being calibrated.
Overflow and Chamber Vents
All Dynacalibrators include an overflow vent to dump excess calibration gas,
ensuring that analyzers sensitive to sample feed pressure receive zero and
span gas at near atmospheric pressure. The overflow vent is therefore usually
left open, or plumbed to an external exhaust point with large diameter tubing.
External devices (filters, etc.) or tubing with too small a diameter on the overflow
vent may cause an undesirable increase of pressure at the analyzer’s input.
The Model 340 is also equipped with a chamber vent. The chamber vent dumps
calibration gas from the permeation chamber when these models are in any
mode other than SPAN / SPAN 1 / SPAN 2. In the ZERO mode, the dilution stream
becomes the zero air supply.
Getting Started