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SMV 3000 Transmitter User’s Manual 1/9960
6.7 AP/GPConf Configuration - PV2, Continued
Background
Internally, the SMV transmitter uses absolute pressure values for all flow
calculations. The value entered in the Atmospheric Offset field is added
to the gauge pressure input value to approximate the absolute pressure.
An inaccurate atmospheric pressure offset value will result in a small error
of the flow calculation.
Use an absolute pressure gauge to measure the correct atmospheric
pressure. A standard barometer may not give an accurate absolute
pressure reading.
PV2 (AP/GP or SP)
Range Values
(LRV and URV)
The Lower Range Value and the Upper Range Value fields for PV2 are
found on the AP/GPConf tab card.
Set the LRV (which is the process input for 0% output and URV (which is
the process input for 100% output for the static pressure input PV2 by
typing in the desired values on the SCT tab card.
• LRV = Type in the desired value (default = 0.0)
• URV = Type in the desired value
(default = 50 psia for model SMA110)
(default = 750 psia for model SMA125)
(default = 3000 psig for model SMG170)
NOTE: Static pressure may be absolute or gauge pressure, depending on the model
SMV 3000 you have selected.
ATTENTION • The range for PV2 is static pressure (as measured at the high pressure
port of the meter body).
• The URV changes automatically to compensate for any changes in the
LRV and maintain the present span (URV – LRV).
• If you must change both the LRV and URV, always change LRV first.
Damping
Adjust the damping time constant for Static Pressure (PV2) to reduce the
output noise. We suggest that you set the damping to the smallest value
that is reasonable for the process. The damping values (in seconds) for
PV2 are: 0.00
d
, 0.16, 0.32, 0.48,
1.0, 2.0, 4.0, 8.0, 16.0, and 32.0
d
Factory setting.
Background
The electrical noise effect on the output signal is partially related to the
turndown ratio of the transmitter. As the turndown ratio increases, the
peak-to-peak noise on the output signal increases. See the Damping
paragraphs in subsection 6.6 for a formula to find the turndown ratio using
the pressure range information for your transmitter.