OHAUS TROOPER, Service Manual

Page: 42 / 70

4-2
CHAPTER 4 TESTING
4.3 PERFORMANCE TESTS
Accurate performance of the Trooper Scale and Trooper Count Scale is determined by a series of three
performance tests. These tests are used to evaluate the scale performance before and after repairs. Each
scale tested must meet the requirements specified in each test as well as the specifications listed in Tables
4-1 and 4-2. Before proceeding with the following tests, all the procedures beginning with section 4. must
be successfully completed and the displayed unit must be set to kg. Set the scale readability to the factory
default setting. This can be done by means of the Setup Menu – Reset function for the Trooper Count Scale
and setting the Trooper Scale to kg. A scale passing each of these three tests complies with Ohaus
specifications.
4.3.1 Repeatability Test
Repeatability is the standard deviation of a set of similar weight readings. To determine the repeatability,
perform the following test:
1. Zero the scale. The reading on the display should be 0kg.
2. Select a test weight near the maximum capacity of the scale and place it on the center of the
pan. Observe and record the reading.
3. Remove the test weight. The reading should return to 0g.
4. Repeat this test for ten readings. Calculate the standard deviation of the ten load readings
using a calculator with statistical capabilities or use the following formula:
Standard Deviation Standard Deviation Standard Deviation Standard Deviation Standard Deviation ( )=
x = weight reading in kg
x = Mean (average) of 10 readings
n = number of readings
A worksheet has been provided for entering the data and calculation results for the Standard Deviation
(Figure 4-3). Step by step instructions for calculating the standard deviation are provided in Figure
4-4 and a sample calculation is provided in Figure 4-5.
√
∑
[ x - x ]
2
n - 1
σ