Appendix F. CPEC300 Series Diagnostics
F-15
If the value of
valve_flow
=
NAN
, this indicates a problem with the valve flow
measurement. The valve flow is inferred from the pressure drop in the sample
(p. 20)
.
Check the value of
valveControl
. This variable determines the size of the
opening of a proportional control valve, from 0 (fully closed) to 1.0 (fully
open). This proportional control valve can be described as an electrically
operated needle valve. In normal operation, when the flow falls below the
setpoint, the CPEC300 will respond by increasing
valveControl
. This
increases the opening in the proportional control valve and allows
valve_flow
to rise to the setpoint. Conversely, if the flow is above the setpoint the
CPEC300 will adjust
valveControl
downward until the flow matches the
setpoint.
If
valveControl
=
0
, this indicates the CPEC300 has turned the valve flow off.
There are several reasons the CPEC300 may shut the valve flow off:
•
No valve is selected
•
Measured valve flow is NAN
•
Low supply voltage (see notes on bit 9)
•
IRGA has been powered down (see notes on bit 8)
If the flow is not at the setpoint, the troubleshooting steps depend on the
situation. There are three cases:
1.
Flow is provided from a cylinder of compressed gas. This is the most
common situation. Make sure the cylinder’s regulator is connected to
the proper fitting on the valve module and that it is regulating the
pressure to 10 ± 5 psig. The value of
valveControl
should be between
0.2 and 1.0. If
valveControl
=
0.2
and
valve_flow
is too high, this
indicates the control valve is unable to provide enough restriction to
limit the flow.
The proportional control valve will be fully closed at any value of
valveControl
below approximately 0.3.
If
valveControl
is
1.0
and the flow is too low and a CPEC300 system is
accessible, check the indicator lights on the valve module. One of the
inlet valve lights (
Zero Air
,
CO
2
Span 1
, etc.) should be illuminated.
The
Flow Control
light should also be illuminated. The brightness of
the
Flow Control
light indicates how hard the proportional control
valve is driven. If
valveControl
=
1.0
this light should be full
brightness (approximately as bright as the light that indicates which
inlet valve is selected). If the appropriate valve module indicator
lights are not illuminated, make sure the connector on the side of the
valve module is connected.
2.
If the H
2
Ospan valve (6) is selected, the flow is not controlled by the
CPEC300 system, but by the dewpoint generator, which pushes flow
through the valve module to the IRGA. The CPEC300 fully opens the
flow control valve by setting
valveControl
=
1
. The acceptable range
for
valve_flow
is between 0.2 and 2.0 LPM. If the CPEC300 is
accessible, check the indicator lights on the valve module as described
above. Also check the tubing connection between the dewpoint
NOTE
Содержание CPEC300
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