Chapter 3 Functional descriptions
SMSO-2-02.03- 15.07.03 41
3.2.8 Flow meter
The flowmeter measures the water quantity in the serving of
coffee. A number of the machines’ functions are controlled by
this measurement. for example the quantity dosing, or indi-
rectly, the heating of the instant heater for coffee.
Function
The flowmeter is built into the supply pipe to the instant heater
for coffee. In principle, it is a small turbine, which, each time it
rotates, produces two electrical pulses in a sensor (Hall ele-
ment) and these are counted by the EHS (Unit control sys-
tem). Approximately 2 millilitres of water are pumped at each
revolution of the turbine wheel. This produces a quantity of
water of 1ml at each pulse, 100 pulses equals 100 ml. The
baffle at the water intake to the turbine chamber causes the
water to reach the turbine blades at a higher speed, thus
ensuring that the turbine wheel is driven safely.
Quantity dosing
The quantities are determined, and the program is controlled
by counting the pulses on the basis of the volumetric dis-
placement for each pulse.
Flow meter
1 Housing
2 2mm dia. baffle
3 Turbine
4 Magnet (2 on rotor)
5 Sensor (Hall element) generating a pulse each time a
magnet passes over it.
Flow meter plug
Check polarity when making the connection. Incorrect polarity
will destroy the flowmeter!
1 black, GND
2 green, pulse
3 white, + 5V
Technical data
Flow volume per revolution: 2 ml
Water quantity per pulse: 1 ml
Operating voltage: 5 V DC
Maintenance
Most frequent faults
Calcium deposits, produces differing amounts of product
dispensed.
Dirt produced by particles: Turbine wheel blocked
Check
The flowmeter is tested indirectly.
Serve a cup of coffee in a suitable container (a measuring
beaker). (Ascertain the amount of product produced)
Make a big change to the programming to alter the
amount of coffee served (at least 20 ml).
Now serve another coffee into the same measuring
beaker. Ascertain the amount of product produced.
The difference in the quantity of product dispensed must
agree approximately with the alteration you made in the pro-
gramming system.
Quantities dispensed in ml and P (P=flowmeter pulses)
NOTE. The actual number of pulses to set is approximately
10-15 pulses higher because in each brewing cycle approxi-
mately 10-15 ml of water is lost as the ground coffee is mois-
tened and the brewing system is evacuated.
1 Small cup (espresso / ristretto)
2 Medium cup (normal coffee)
3 Large cup
NOTE: If the flowmeter is not functioning or if no pulses are
reaching the control system, the control system will go back to
the last outlet time used, thus controlling the quantity dispen-
sed. “Flowmeter defect” appears on the display.
Drawing symbol
Illustration
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