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9.4. Working Principle of the Electric Parts
The OMEGA-HB Ball Hardness Tester employs a new loading procedure other than the
conventional pendulum loading. The new loading system uses a closed loop control system,
which is controlled by CPU. A sensor controls the signal and step motor for loading. PHILIPS
P89C51RD2 is used as the CPU. AD 574 chip is used as AD converter, with a typical conversion
time of 25
μ
s and non-linearity of ±1/2LSB. BB company’s INA114AP is used as the algorithm
amplifier.
The electric working principle can be described as following: Electronic signals are collected by
LF-3T spoke type sensor and, after being amplified by INA114, output to AD574 for AD
conversion. Then the analogue voltage signals are changed into the 12-digit signals and sent to
CPU for computation processing and finally used to control the motor’s loading, dwell and
unloading actions.
There are 10 test loads (62.5, 100, 125, 87.5, 250, 500, 750, 1000, 1500, and 3000 kgf) available
for use on OMEGA-HB Digital Ball Hardness Tester, the lower 5 load (62.5
～
250 kgf) have a
resolution of 0.1kgf, and the upper 5 loads (500
～
3000 kgf) have a resolution of 1 kgf, to ensure
the test loading force is more stable and reliable,
The tester uses a Japan made DMF-50081 320×240 LCD as display, user may choose desirable
test load and indenter on the display after start-up of the tester. Other data including D1 and
D2 (indent diameter), HBW hardness and corresponding converted value are also shown on the
display. After completion of the test cycle, the data may be output through RS232 serial
interface into a PC’s Hypertrm terminal for display or printing out, or directly saved into CPU’s
internal memory for permanent storage.
There are two limit switches for the ascending and descending movement of lifting screw
respectively. A magnetic sensor base is installed at rear of the main lever (see figure). Two
proximity switches are installed on the right side near to the rear cover to control the initial
position of main lever and the total stroke. Both proximity switches (A and B) are placed in
adjacent positions near the switch A. After powering on the tester the motor lifts the lever
whereby the switch A will receive signal from magnetic sensor and is feed to the CPU.
Thereafter the motor will stop at first and then rotate in counter direction for several turns to
return the lever back to its original position. DO NOT change the position of proximity switches.
Switch B is the lower limit switch for lever’s movement, i.e. when the lever moves approaching
