AEC OS Series Gravimetric Batch Blenders - Manual (Page 90)

Page 89 of 118
The mix hopper high level signal is generated by a proximity level sensor
located in the right hand portion of the mixer chamber (viewing from the
mixer door). This sensor requires 110 volts AC and acts as a normally
open switch. When there is no material covering the front of the sensor,
the circuit is open. If material covers the front of the sensor, the circuit
closes. This closure causes SSR-8 to energize. SSR-8 then converts the
110-volt signal to a +5 volt DC signal for the CPU board to read.
Load cells require +5 volts DC to operate. This is known as the load cell’s
excitation voltage. Using the + 5 volt DC, the load cell generates a 0 - 10
millivolt signal that is returned back to the CPU board A/D input. This
signal is proportional to the amount of weight on the load cells. The on
board A/D (analog to digital) converters on the CPU board convert this
signal to digits for the computer to read. The digits are referenced to the
zero weight digit reading and the calibration weight digit reading that was
input during the calibration procedure on the load cells. Based on this
information, the computer determines the precise weight in the weigh
hopper.
6-6-4 Output Signals from Control Panels
The OS/OA blending system uses several output control signals to
control the process. All of these are very similar in nature, the first of
which is the mixer motor control.
The mixer motor control is activated via a control port located on the CPU
board PC-1. SSR-1 is a power relay and is sized to handle the amount of
current required to drive the mixer motor on smaller units. If the mixer
motor is large (“HC” style OA-030/060 only), such as on the larger
models, the SSR-1 can power a second motor contactor located in the
panel on the rear of the blender. (This will power the mixer from a second
power line, to cut the voltage drops to the computer panel when the mix
motor starts.)
Note:
This is a special setup to allow operation when plant wiring to the
blender cannot carry the load without voltage drops. HydReclaim
recommends that an un-interruptible power supply (UPS) be
installed to provide steady power for the computer circuit.
To protect this circuitry in the event of a mix motor overload, there is a
control fuse mounted in the side panel of the blender.