Sensia CLIF MOCK CD-20 - Motor Control Assembly

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CD-20 Sample Probe Controller
5. Reconnect input power to the CD-20.
6. Hold a 100-ml graduated beaker (or other applicable measuring device) under the probe’s discharge.
7. Activate the switch repeatedly to collect 10 samples, 1.5 cc each.
Motor Control Assembly
The CD-20 motor control assembly (Figure 1.2, page 6) consists of a control card and power board
mounted to a ring, which in turn, is mounted to the back of the CD-20 gear motor.
Control Card Functions
When an input pulse from either the repeat-mode timer or an external pulse source is received, a speed
command is output to rotate the motor. Armature feedback controls the speed of the motor at about 12 rpm
and current feedback limits motor current to 3 amperes.
The proximity switch input amplier provides the signal to stop the motor.
The I-LIMIT LED is on when the drive is in current limit, which is normal during acceleration.
The PROX (“Hold”) LED is on when the motor is stopped.
Power Board Functions—12VDC and 24VDC Controllers
The 12VDC and 24VDC power boards provide the following functions:
• Fuse F1 (2-amp, fast-acting) provides short circuit protection. ZD1, a 33V “crowbar” zener diode, pro-
vides over voltage protection for the rest of the circuit.
• Diode D2 prevents current ow if +12/24VDC power is connected to the common terminal and a ground
is connected to the +12/24VDC terminal.
• Q4, an LT1074CT switching regulator and associated circuitry efciently convert the +12/24VDC into a
regulated +6.3VDC motor supply voltage.
• The control card uses motor armature feedback to set the speed command to the motor driver power FET
Q2.
• A stop command from the control card to Q1 provides motor braking which prevents the motor from
coasting past the stopping point.
• R6 is the motor current feedback resistor. The motor current is limited to 3.0 amps.
• Fuse F2 (2-amp, slow blow) will open in less than 1 minute if the motor is stalled (locked rotor).