ADV Service Manual P/N 83020790 A
Ohaus Corporation
www.ohaus.com
12
2.6 TRANSDUCER DESCRIPTION
Figure 2-2 illustrates a typical Transducer used in the Adventurer balances. The Transducer is attached to the
case of the balance. The force of a weight placed on the weighing Pan is exerted on the Hanger which is guided
by the Upper and Lower Flexure Arms. The Load Flexure transfers the force vertically to the Ratio Beam. The
Ratio Flexures form a pivot for the Ratio Beam.
Any mass placed on the Pan applies a downward force to the Load Flexure by means of the Center Post. The
Load Flexure pulls down on the front end of the Ratio Beam which pivots, pulling the Force Coil up into the air gap
of the Magnet. The upward movement of the Vane (which is connected to the Ratio Beam) is detected by the
Position Sensor. The Position Sensor contains one light emitting diode (LED) and two photo resistors. When the
Vane moves, the amount of light is varied, causing one of the photo resistors to change its resistance value. The
resultant signal goes into an amplifier to be amplified and filtered. The signal then goes through a current amplifier,
then fed to the force coil which interacts with the Magnet returning the Ratio Beam to the null position. In the null
position, light should strike each photo resistor equally. The entire process takes approximately 4 seconds from
the time any mass is placed on the Pan to achieve a stable reading.
The mechanical zero of the system is moved to the approximate middle of the measuring range by the Counter
Weight. Displacement of the Position Sensor Vane from the normal position results in a current change in the
Force Coils. The Force Coils are located in the field of the permanent Magnets which are mounted on the
Transducer Base. This means that with a 50% load on the Pan, the Ratio Beam is in equilibrium and the sum of
the forces from the Force Coils is zero. The temperature sensitivity of the Permanent magnets is compensated in
the electronics by a Temperature Sensor which is physically mounted on the magnet assembly.
Figure 2-2 Transducer Assembly
2.7 BLOCK DIAGRAM CIRCUIT DESCRIPTION
Figure 2-3 illustrates the Adventurer electronic circuitry as a block diagram.
2.7.1 Main PC Board
Power Supply
Power is supplied to the balance through an AC/AC adapter which provides 12 Volts ac or DC/DC adapter which