D-Series Syringe Pumps - Isco

D Series Syringe Pumps
Section 4 Theory of Operation
high enough for the power dissipated by the transistor to destroy
the device. To protect the high side drivers in this braking condition,
control software pulses the direction signal. This allows
the current to alternately build up to a safe level and decay
between pulses, limiting the power dissipation of the device.
Below approximately 800 RPM of the motor, the direction signal
functions without this pulsing effect and correctly indicates the
desired direction of motor drive.
Pump Type
1000D
500D
260D
100DM
100DX
65D/DM
Flow Rate at 800 rpm
40.582 ml/min
20.295 ml/min
10.642 ml/min
3.0888 ml/min
6.1776 ml/min
2.7176 ml/min
Referring to the components connected to the gate of Q106, two
additional circuit functions are present. Negative feedback compensation
is provided by R137 in series with C130. They limit the
switching speed of Q106 and prevent oscillation. A current-limiting
circuit, consisting of Q111, R112, and R139, limits the
current through Q106 to about 6 amps by reducing the gate drive
voltage in the same manner described previously for Q107, R113,
and Q103. In normal operation, when Q106 or Q108 are switched
off, energy stored by the motor inductance and filter inductors
(L1 and L2) may maintain current flow until the next drive
pulse. If current is circulating in this manner through diode
CR105 when Q106 is switched on, there will be a short delay
after current reversal before CR105 turns off.
Q111 limits the current from the supply (+VM) through CR105
and Q106 while CR105 is in the low impedance state.
Inductors L1 and L2 with capacitor C1, form a low pass LC filter
between the power amplifier and the motor. Capacitors C2, C3,
and C4 attenuate motor brush electrical noise. Relay K101 is
switched by the controller and serves to connect the motor to the
power amplifier when energized. When released, it connects
R115 across the motor terminals to dissipate energy and brake
the motor. An electromechanical brake (shown electrically as L3)
is wired in parallel with K101 to allow the pump to hold pressure
without motor rotation when the power amplifier is disconnected
or the instrument is without power.
To activate the relay and release the brake, the motor enable
signal must be pulled low by the controller. This signal is
series-wired through the controller front panel ON/STANDBY
switch and a transistor switch under control of the microprocessor.
This allows both the operator and the microprocessor to
disable the motor if either detects a problem.
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