D-Series Syringe Pumps - Isco

D Series Syringe Pumps
Section 4 Theory of Operation
4.2.1 Electric Valve Interface Incorporated into the Series D Controller is a bus interfaced
circuit board for the Electric Valve Package.
Valve Motor Control
The valve is operated by a direct current, permanent-magnetic-field
gear motor. The motor provides rotary motion to open
and close the valve.
Note
Electric valves are not available for the 65D pump. Please consult
the factory for options.
The valve is closed to a preset torque determined by controlling
the motor current during the closing cycle. In this type of motor,
the output torque is proportional to motor current. Therefore,
current control provides satisfactory torque control.
When the valve is opened, the motor rotates a fixed angular
amount from the closed position. The motor is operated at a constant
speed for the fixed time required to rotate the desired
amount.
Circuit Description
Microprocessor Interface
Relays
Motor Drive Control
(Refer to the Interface Schematic and the Depressurization Valve
Schematic.)
The valve control and sensing signals interface to the controlling
microprocessor through U206, an 82C55A integrated circuit.
Ports A and C are configured as outputs. Port B is configured as
eight inputs. Each output is buffered through a section of a 2803
Darlington transistor driver chip. The outputs of port A select a
motor to be operated, select the direction of operation, and switch
the power circuitry on or off.
The motor selection and direction functions are implemented by
relays. Six DPDT relays are configured to select the desired
motor and an associated current limit setpoint potentiometer.
The current setpoint potentiometer is located on the back of the
valve motor so that controllers can be exchanged without disturbing
the valve torque calibration. A seventh DPDT relay,
K204, switches the motor drive polarity, to select the motor drive
direction.
A reference voltage circuit provides the setpoint for the current
control circuit. Voltage reference U203 is adjusted to 2.50 volts
by R212 and is buffered by U202B. The reference voltage is
divided to provide the current setpoint signal. R210 and the
potentiometer (which is R101 for Depressurization 1 valve) set
the maximum current the drive circuit will provide.
Motor current is switched and regulated by FET Q01. Q01 is
mounted on the controller rear panel for the purpose of heat dissipation.
The motor current also flows through R204, which is in
series with Q01. R204 generated the current feedback signal
which is a voltage proportional to the motor current.
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