Datasheet

40
1. Check regulators and flow adjustment valves
before introducing the fluid.
If pressure or flow rate beyond the specified range are applied
to the switch, the sensor unit may be damaged.
[For air]
2. The fluids that the switch can measure
accurately are nitrogen and dry air.
Please note that accuracy cannot be guaranteed when other
fluids are used.
3. Never use inflammable fluids.
The flow velocity sensor heats up to approximately 150°C.
4. Install a filter or mist separator on the upstream
side when there is a possibility of condensate
and foreign matter being mixed in with the fluid.
The rectifying device built into the switch will be clogged up and
accurate measurement will no longer be possible.
[For water]
5.
The fluid that the switch can measure accurately is
water. Also, combination of equal parts water/ethylene
glycol (50/50%) can be used if its temperature is high.
Please note that accuracy cannot be guaranteed when other
fluids are used.
6. Never use inflammable fluids.
7. Install a filter on the inlet side when there is a
possibility of condensation and foreign mat-
ter being mixed with the fluid.
If foreign matter adheres to the switch’s vortex generator or
vortex detector, accurate measurement will no longer be
possible.
1. After the power is turned on, the switch’s
output remains off while a message is
displayed. Therefore, start the measurement
after a value is displayed.
2. Perform settings after stopping control systems.
When the switch's initial setting and flow rate setting are
performed, output maintains the condition prior to the settings.
3. Do not apply excessive rotational force to the
display unit.
The integrated type display unit can rotate 360°. Rotation is
controlled by the stopper; however, the stopper may be
damaged if the display unit is turned with excessive force.
[For air]
4. Be certain to turn on the power supply when
the flow rate is at zero.
Allow an interval of 10 minutes after turning on the power, as
there are some changes in the display.
5. Flow rate unit
The switch measures at mass flow rates without being
influenced by temperature and pressure. The switches use
l/min as the flow rate indicator unit, in which the volumetric flow
is substituted for mass flow at 0°C and 101.3 kPa (nor). The
volumetric flow rate at 20°C, 101.3 kPa, and 65%RH (ANR) can
be displayed with the high flow rate type switches for air.
Others
Measured Fluid
Warning
Warning
Detection principle of digital flow switch for air
A heated thermistor is installed in the passage, and fluid absorbs heat from the
thermistor as it is introduced to the passage. The thermistor's resistance value
increases as it loses heat. Since the resistance value increase ratio has a
uniform relationship to the fluid velocity, the fluid velocity can be detected by
measuring the resistance value. To further compensate the fluid and ambient
temperature, the temperature sensor is also built into the switch to allow stable
measurement within the operating temperature range.
Fluid velocity
detection element
Temperature
compensation element
Detection principle of digital flow switch for water
When an elongated object (vortex generator) is placed in the flow,
reciprocal vortexes are generated on the downstream side. These vortexes
are stable under certain conditions, and their frequency is proportional to
the flow velocity, resulting the following formula.
f = k x v
f: Frequency of vortex v: Flow velocity k: Proportional constant
(determined by the vortex generator's dimensions and shape).
Therefore, the flow rate can be measured by detecting this frequency.
Fluid
Vortex generator Vortex detector
This flow switch uses l/min
as the flow rate indicator
unit. The mass flow is
converted and displayed
under the conditions of 0°C
and 101.3 kPa.
The conversion conditions
can be switched to 20°C and
101.3 kPa with high flow
type switches.
1. Perform periodical inspections to ensure
proper operation of the switch.
Unexpected malfunctions may cause a possible danger.
2. Take precautions when using the switch for
an interlock circuit.
When a pressure switch is used for the interlock circuit, devise a
multiple interlock system to prevent trouble or malfunction, and verify
the operation of the switch and interlock function on a regular basis.
3. Do not disassemble or perform any conversion
work on flow switches.
Maintenance
Warning
Measured Fluid
Warning
Contact SMC regarding the specifications for clean environment.
Specific Product Precautions 3
Be sure to read before handling. Refer to page 37 for safety instructions.
Series PF2A/PF2W