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PLF2105 Flow Sensor
The Posifa PLF2105 is a low-cost liquid flow meter designed for rates of 50 to 700 ml/min.
- Use with 1/4" ID tubing
- 5V Power supply
- I2C digital output
- 5ms response time
These specs should be ideal for use in espresso machine flow profiling.
To minimize the difficulty / invasiveness of installing a flow sensor, COM-GND is attempting to install it on the inflow side of the pump.
In initial testing, one issue is that the pulsation caused by common vibratory pumps like the Ulka cause peek flow rates that exceed the 700ml/min maximum rate of the sensor. This issue is especially prevalent when the pump is running under nominal load (< 2 bars pressure).
This is a known limitation with flow sensing and the common solution is to add a pulsation damper into the system.
There are some existing dampers designed for Ulka pumps (e.g. one made for Quick Mill machines. However, these are designed to be attached to the outflow of the pump and make the installation very complicated.
There is another type of damper call a "discharge tube" that uses a simple tube and flow restrictor arrangement (such as this one). The advantage being that this can be installed inline with the flow sensor. This page also offers some guidance to the construction.
A length of soft silicone tube between the sensor and the pump will act as a simple damper. Combining it with a flow restrictor will help ensure that the max rate of the sensor is not exceeded.
In → Sensor → [Restrictor] → Damping Tube → Pump
If that does not sufficiently reduce the pulsation, and simple damper reservoir made from a Bulb dropper will be tested as well.
Flow Restrictors
- Note: Sensor max flow is .7L/min or about .15G/min
- Fixed: https://www.mcmaster.com/2258N35-2258N23/
- Variable: https://www.mcmaster.com/2897N11/
Soft, food-grade silicone-tube for use as "discharge tubing"
Bulb Dropper for use as a damper vessel
Tee Connector to connect Bulb Dropper