Watson-Marlow 720DuN User Manual 67
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 propor-
tional 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 2.133 Hz/rpm—128 pulses per pumphead revolution. The
pulse train from the pump can be used to calculate the speed of rotation or to deter-
mine 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.
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