Photocell
Controls
Circuits
Indicators
LED
Flag
Magnet
Magnet
Sample
Balance Beam
Taut Band
Suspension
and Torque Motor
Coil Connection
Rotation at Axis
of Beam &
Coil Assembly
Torque
Motor Coil
Tare loop
“A” loop
“B” loop
1
Section 1 Principles of Operation
The Cahn C-34/C-35 is a very sensitive weight and force measurement instrument. It is designed
for weights and forces up to 3.5 grams and is sensitive to changes as small as 0.1 micrograms.
The balance may be described as a force-to-current converter. It consists of (1) a balance
beam mounted to, supported by, and pivoting about the center of taut ribbon; (2) a torque
motor coil located in a permanent magnetic field and also mounted to the taut ribbon;
(3) sample suspension fixtures; (4) a beam position sensor system; and (5) controls, circuitry
and indicators (See Figure 1).
Weights or forces to be measured are applied to the sample (left) side of the beam which
produce a force about the axis of rotation. An electric current flowing in the torque motor also
produces a force about the same axis which is equal and opposite to the force from the beam,
if the beam is at the beam reference position. This reference position is detected by the beam
position sensing system. A greater force on the beam will require a greater opposite force from
the torque motor in order to keep the beam at its reference position. Therefore, the current
necessary to produce the required torque motor force is a direct measure of the force on the
beam. The process of calibration allows this current to be measured in units of weight (grams).
Figure 1: Principles of Operation
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
