Table of Contents
Advertisement
200/202 Series Flowmeters and Controllers Instruction Manual
Operation
The standard instrument output signal is 0 - 5 VDC and is proportional to the flow i.e., 0
Volts = zero flow and 5 Volts = 100% of rated flow. The 4 - 20 mA option is also proportional to flow, 4
mA = zero flow and 20 mA = 100% of rated flow. It is recommended that all connections be checked for leaks
after installation. Do this by pressurizing the instrument (do not exceed 500 psig unless the Flowmeter is
specifically rated for higher pressures), applying a diluted soap solution to the flow connections, and
monitoring the connections for bubbles of escaping gas.
WARNING: Make sure the work area is safe (de-pressurized) before installing a flow
instrument. Make sure emergency shutoff or pressure release valves are available for safe
working conditions. Do not exceed 500 psig unless the flowmeter is specifically rated for
higher pressures
2.6.1.
Operating Conditions
For proper operation, the combination of ambient temperature and gas temperature must be such that
the flow meter temperature remains between -20 and 70°C. The most accurate measurement of flow will
be obtained if the flow meter is zeroed at operating temperature as temperature shifts result in some
zero offset. The HFM-200/HFC-202 Series is intended for use in non-condensing environments only.
Condensate or any other liquids which enter the flow meter may destroy its electronic components.
2.6.2.
Zero Check
Turn the power supply on if not already energized. Allow for a 1 hour warm-up. Stop all flow through
the instrument and wait 2 minutes. Caution: Do not assume that all metering valves completely shut off
the flow. Even a slight leakage will cause an indication on the meter and an apparent zero shift. For the
standard 0 - 5 VDC output, adjust the zero potentiometer located on the inlet side of the flowmeter until
the meter indicates zero. For the optional 4 - 20 mA output, adjust the zero potentiometer so that the
meter indicates 4 mA. This zero should be checked periodically during normal operation. Zero
adjustment is required if there is a change in ambient temperature, or vertical orientation of the flow
meter/controller.
2.6.3.
High Pressure / High Density Option
When operating at high pressure or with high density gases, the increased density of gas will cause
natural convection to flow through the sensor tube if the instrument is not mounted in a level position.
This natural convection flow will be proportional to the system pressure. This will be seen as a shift in
the zero flow output that is directly proportional to the system pressure. This zero shift can be corrected
by adjusting the zero potentiometer after mounting the flow controller in its final operating position. See
section 2.4.1 and 2.6.2. Additionally, because the specific heat of a gas changes with pressure, an
associated error is introduced with increased pressure. It is directly proportional to the change in specific
heat versus pressure for that particular gas. For helium, there is virtually no change in indicated output;
for nitrogen, the indicated output will increase at approximately 0.0067%/psi, which is the pressure
coefficient. So we have:
EAR99 Technology Subject to Restrictions Contained on the Cover Page
������������ �������� =
( 1 + (���������������� × ���������������� ����������������������) )
������������������ ��������
Page 16 of 27
Advertisement
Table of Contents
