MJ400155E1
8.Operating
8.1 Operating Conditions
For proper operation, the combination of ambient temperature must be such that the flow
meter temperature remains between 0 and 60℃. 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-201/HFC-203 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.
8.2. Zero Check
Turn the power supply on if not already energized. Allow for a 1hour 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 0-5VDC output, adjust the zero
potentiometer located on the lower inlet side of the flow meter until the meter indicates zero.
For the optional 4-20mA output, adjust the zero potentiometer so that the meter indicates
slightly more than 4mA, i.e. 4.03 to 4.05mA. This slight positive adjustment ensures that
the 4-20mA current loop transmitter is not in the cut-off region. The error induced by this
adjustment is approximately 0.3%of full scale. 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 orientation of the flow meter / controller.
8.3 Blending of Gases
In the blending of two gases, it is possible to maintain a fixed ratio of one gas to another. In
this case,the output of one flow controller is used as the reference voltage for set point
potentiometer of a second flow controller. The set point potentiometer then provides a
control signal that is proportional to the output signal of the first flow controller. The set
point potentiometer then provides a control signal that is proportional to the output signal of
the first flow controller,and hence controls the flow rate of the second gas as a percentage
of the flow rate of the first gas.
EXAMPLE:Flow controller A has 0-100slpm range with a 5.00V output at full scale. Flow
controller B has 0-10slpm range with a 5.00V output at full scale. If flow controller A is set at
80slpm,its output voltage would be 4.00V(80slpm/100slpm x5.00V=4.00V).If the
output signal from flow controller A is connected to the command potentiometer of flow
controller B,it then becomes a variable reference voltage for flow controller B proportional