D-Series Syringe Pumps - Isco

D Series Syringe Pumps
Section 4 Theory of Operation
Analog-to-Digital Converter
Circuit
Motor Control
A 16-bit analog-to-digital converter U129 reads eight multiplexed
analog inputs, which include pump pressure signals and
general analog interface signals used for external control. The 16
bits of information from U129 is transferred to the CPU in two
successive reads. Pin 33 of U129 selects the 8-bit bus mode. The
4051 CMOS multiplexer (U130) input is selected under microprocessor
control by setting the three output pins P1.4, P1.5, and
P1.6. The 5 volt signal is level translated to 12 volts by U131, a
4504. CR117 protects the circuit from excessive swings and
floating inputs. R126 with C144 and C169-C175 filter the inputs
to prevent aliasing. The selected input is buffered by operational
amplifier U132A. U132B inverts, level shifts, and scales the
input signal to match the bipolar input range of A/D circuit U129
determined by voltage reference circuit U133. A circuit composed
of diodes and zener diodes prevents this signal from exceeding
the analog supplies of U129. The three pump pressure signals
are scanned at a rate of 500 HZ, and all other signals at a rate of
100 HZ. These signals are then filtered by software. A conversion
is initiated by a low pulse on the HOLD signal (pin 1) of U129,
and the end of conversion signal at pin 38 activates an interrupt
routine to read the value. These signals should pulse at a frequency
of 2.0 kHz.
The syringe pump motor speed control is entirely a digital
control system. Both the pressure and flow rate controls are
software implemented via the controller module. Feedback and
control elements are duplicated for three pump control, so only
the pump A controls will be described.
The syringe pump module includes a power amplifier to interface
the digital controls to the direct current, brush type electric
motor. The pump full and pump empty positions are detected by
optoelectronic sensors in the pump module, and the signals
connect to P110 of the controller through the pump control cable.
These signals are labeled ULA (upper limit pump A) and LLA
(lower limit pump A) for cylinder empty and full, respectively.
The piston travel limit signals are connected to port 0 of the
microprocessor, U104. For more information see section 4.6,
Piston Travel Limit Sensors.
The motor drives an optoelectronic quadrature position sensor
which encodes the angular position of the motor, see section 4.6,
Quadrature Motor Angular Position Sensors. The two
quadrature position feedback signals (TACHAA AND TACHAB)
connect to P110 via the pump control cable. These signals feed
the count inputs of U121, an LS7166 quadrature decoder
up/down counter. The value of this counter represents the
angular position of the motor. The microprocessor reads U121 via
the 8-bit bus and compares this feedback to the desired motor
position. A motor drive, pulse-width modulated (PWM) signal
and a motor drive, direction signal are then generated by the
microprocessor to drive the motor to the correct position.
D Series Syringe Pumps
Section 4 Theory of Operation
4-4