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Watson-Marlow 620DuN and 620Du User Manual 61
age in the Setup menu. Otherwise the reference voltage supply from the Rem-pot
connector will be overloaded and will not provide a full 5V or 10V.
The speed of the pump as set by Analogue 1 is scaled in proportion to the signal
from Analogue 2 according to the formula y=as, where a is the speed set by
Analogue 1, s is the scaling set by Analogue 2 (0V or 4mA = 0, increasing linearly
to 10V or 20mA = 1), and y is the scaled rotation speed. If Analogue 2 has been set
for an inverted response, the reverse is true. See 18.2 Analogue in the Setup menu.
22.5 Speed: analogue output
An analogue voltage output signal is available on
the Tacho output connector (J11), between the V
terminal and the 0V terminal. The voltage is direct-
ly proportional to the pumphead rotation speed.
0V = zero speed; 10V = maximum allowed speed.
A current analogue signal within the range 4-
20mA is available between the mA terminal and
the 0V terminal. The current is fixed and directly
proportional to the pumphead rotation speed. 4mA
= zero speed; 20mA = maximum allowed speed.
Note: If the mA output is to be used for reading
from a multimeter, a 250Ω resistor is required in series.
22.6 Tachometer frequency output
A tachometer frequency output is available on the Tacho output connector (J11),
between the freq terminal and the 0V terminal. It provides a +5V square wave
pulse, maximum 0.5mA, the frequency of which is directly proportional to pumphead
rotation speed. It provides 5.578 Hz/rpm - 334 pulses per output shaft revolution.
The pulse train from the pump can be used to calculate the speed of rotation or to
determine the number of pumphead revolutions. This output has the required
strength to be effective up to 3m from the pump. Longer cable runs require signal
amplification.