Ashcroft ATE-100 Handheld LCD Digital Calibrator - Manual (Page 25)

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Revision 4.6 3/2004
of operation.
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Step 2 Connect the output lines from the device under
test to the miniature banana jack inputs on the front of
the HHC. Use the mA and COM jacks for current devices
and the V and COM jacks for voltage output devices.
Step 3 Make the necessary plumbing connections
using a Tee fitting to allow input of applied pressure to
both the HHC and the device under test.
Step 4 Perform testing in accordance with the number
of calibration points required for the device to be tested.
Step 5 To exit the percent mode press the percent key.
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The HHC will respond by returning to basic pressure or
temperature measurement activities.
Section 14.0 Flow Velocity and Flow Volume
Measurement Background
The HHC used in conjunction with a pitot tube or an
annubar has the ability of measuring the flow volume or
flow velocity of a clean, dry gas. The HHC must be used
in with a GQS-1 low differential pressure Quick Select
module to perform the flow measurement function.
The accuracy of a flow measurement is a function of
a number of contributing factors. These are; the basic
accuracy of the differential pressure measurement, accu-
racy of the pitot tube or annubar in use as it relates to
the K factor supplied by the manufacturer of the device
and the accuracy of the correction being made for the
air density. It is not possible to provide an all inclusive
accuracy statement for flow measurement activities.
Steps that can be taken to maximize system flow mea-
surement accuracy include:
1 – Calculation and input of the actual air density for the
media to be measured. The air density is a function of
temperature, humidity, barometric pressure.
The velocity equation (ft/min) is as follow:
where:
dpw = differential pressure in inches of water
Adw = the air density
The air density can further be calculated through
employing the following equation:
dpw
V = 1097 x K x
√
Adw
A
d
= 0.07649 x ( Pa/14.73) x [520/(T+460)]
where:
Pa a = the absolute pressure in duct in psia
T = air temperature in duct in degrees Fahrenheit
Flow Volume = (velocity x duct area)/144
2 – Purchase of a characterized and certified pitot tube
or annubar with a K factor determined for the specific
probe to be used.
3 – Purchase of the highest accuracy differential pres-
sure Quick Select module available.
Section 14.1 Set Up for Flow Velocity and Flow
Volume Measurement
In preparation to perform flow velocity and volume
measurements the operator should have the following
information available for entry during the set up of the
application on the HHC.
K factor Provided by the manufacturer of the flow
probe to be used.
Air density A default value has been programmed
into the HHC in the event that a more
accurate one cannot be calculated.
Duct area For air volume measurement the area of
the duct in which measurements are to be
taken must be calculated.
A GQS-1 differential type (dual process connection)
Quick Select pressure module must be used for flow
measurement activities.
Basic keypad functions such as damping, tare, min/max
recall, mA/V measurement display, battery check, dis-
play hold, data logging, zero and port select are avail-
able for use during flow measurement activities. Consult
the appropriate sections of this manual for information
on the set up and use of these product functions.
For flow measurement follow the steps outlined in the
sections corresponding to the type of flow measurement
(velocity or volume) to be performed.
Section 14.2 Flow Velocity Measurement
Step 1 With the HHC on and displaying pressure mea-
surement values press the flow key.
FLOW
The HHC will respond by displaying:
Flow
Velocity Volume
Step 2 To perform flow velocity measurements select
the word velocity using the left/right arrow keys. When
selected the word velocity will flash.
Flow
Velocity Volume