MTS TW Elite - Manual (Page 78)

Configuring the settings that affect polarity
When designing your test, use the following procedure to ensure that the settings that affect polarity are
appropriate:
1. Import the resources that are required by your test.
2. If your load frame has upper and lower workspaces, select the desired workspace.
3. For each float signal, select the polarity that produces the desired output.
4. For each Float Signal, select the desired Effect of Increasing Extension. You can determine the
appropriate setting by adding a meter for each signal, installing a disposable specimen, increasing
extension, and then observing how the signal output changes.
Note:
All command activities in your test that have the Direction property set to Auto will use the
Effect of Increasing setting to determine which direction the crosshead must travel to reach the
termination condition specified in the activity.
If the Direction setting of a command activity is either Increase or Decrease, the crosshead will
move in a direction that will either increase or decrease the control-mode feedback signal value
regardless of whether that movement will ever satisfy the activity’s terminal condition.
User Scenario: Configuring polarity for a system equipped with dual workspaces
For example, consider a scenario in which you want to design a tension test that uses a system equipped
with dual workspaces. While most of your specimens will break when approximately 5 kN of force is applied,
you know that some specimens will break when less than 1 kN of force is applied.
Instead of simply installing the 10 kN load cell into the lower workspace and only using the lower workspace
to test all of your specimens, you install a 1 kN load cell in the upper workspace for use when testing the
weaker specimens. Now, you can test the weaker specimens in the upper workspace and take advantage
of the improved resolution that the smaller 1 kN load cell offers.
Next, you want to ensure that your polarity settings are correct. First, you import all unused resources into
the test. Since you are designing the test in the lower workspace, you ensure that the lower workspace is
selected. Because you are performing a simple tension test and you want the values in the scope and
data acquisitions to become more positive as you apply tensile force, you leave the Polarity setting at the
default value of Normal and the Effect of Increasing Extension at the default value of Value Increases.
However, if you wanted the load signal to become more negative as tensile force is applied, you would
change Polarity to Inverted. Then, because you changed the polarity to inverted, you would need to
change the Effect of Increasing Extension on the Load float signal to Decreases Value.
When you are finished designing the test, you want to validate your test to ensure the results are what you
expect. So, you insert a disposable specimen into the lower workspace and run the test. To ensure that
the upper workspace produces the desired output, you select the upper workspace, insert a disposable
specimen, and then run the test and observe the result.
Debugging
This section contains considerations and techniques test designers should be aware of when creating,
testing, and debugging test procedures.
78 | MTS TestSuite
Design Guidelines