D-Series Syringe Pumps - Isco

D Series Syringe Pumps
Section 4 Theory of Operation
The motor supply voltage +VM is switchable between two levels
under control of the microprocessor. To allow a greater motor
speed dynamic range, the motor supply voltage is switched to
better match the motor operating speed. Motor voltage select
relay K102 switches the power rectifier between a half bridge
and full-bridge configuration to provide two voltage selections
which differ by a factor of two. The relay is switched to the full
bridge configuration above 3000 RPM. In constant pressure
mode, K102 is left in the full-bridge (high voltage) setting at all
speeds. The motor drive circuit is somewhat electrically isolated
from the rest of the instrument, except for R123, a 47k ohm
resistor between motor common and earth ground. The +12-volt
supply for the power amplifier logic is referenced to the motor
common rather than instrument common. This supply is generated
by a voltage regulator circuit drawing its supply from the
motor supply voltage. Zener diode CR102 with diode CR101 and
R114 provide the reference base drive voltage for Q101 which is
configured in the emitter-follower configuration. Q101 thus acts
as a current amplifier at 12-volts fixed output.
The remaining transformer windings supply power for + and -
15-volt, 5% regulators and an adjustable 5-volt supply. Since the
5-volt supply is used as a reference by the microprocessor A/D
converter, it is adjusted to a tighter tolerance than the 15-volt
supplies.
4.4 Pressure Transducer
and Amplifier
To sense cylinder pressure there is a strain gauge built into the
cylinder cap. The strain gauge is a 120 ohm bridge with a sensitivity
that relates to the pressure. The table below lists the
approximate sensitivity of each pump model. The strain gauge is
connected to a -5.00 volt reference supply (CR51 and U51B), a
preamplifier (U52), and a final amplifier (U51A), all located on a
circuit board enclosed at the top of the cylinder.
Pump Model
1000D
500D
65DM, 100DM/DX, 260D
65D
Approximate Sensitivity
100mV/137.89 bar
100mV/344.8 bar
100mV/689.5 bar
100mV/1379 bar
The pressure amplifier gain is adjusted by R53 to provide a
signal of 2-volts per 68.95 bar for the 500D, or 1-volt per 68.95
bar for the 65DM, 100DM/DX, and 260D, and 0.5 volt per 68.95
bar for the 65D. This pressure signal is used for the pressure
display, pressure limiting, and as feedback for constant pressure
regulation. Analog pressure output jacks are located on the rear
panel of the pump module. The two outputs are scaled for ranges
of 1.0-volts per 68.95 bar and 0.10-volts per 68.95 bar. These
outputs are not adjusted by the automatic pressure zero software
which affects the pressure display and control at the controller.
For this reason, these outputs will disagree with the controller
display by the amount of the offset.
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