23-2
IM WT1801-01EN
23 Other Features
Auxiliary Input (Aux)
• All: You can enable or disable the NULL feature for the Aux1 and Aux2 signals at the same time.
• Aux1, Aux2: You can enable or disable the NULL feature for the Aux1 and Aux2 signals separately.
NULL Status (Status)
Enable or disable the NULL feature for each input signal
• ON:
When you press NULL, the WT1800 sets or updates the NULL value. Afterwards, the NULL value is
used to correct the measurement function values.
• Hold:
The function of this key varies depending on whether the NULL value has yet to be set or has
already been set.
• When the NULL value has yet to be set
When you press NULL and enable the NULL feature, the WT1800 sets the NULL value. Afterwards, the
NULL value is used to correct the measurement function values. If you press NULL again, the NULL
feature is disabled, but the WT1800 saves the specified NULL value.
• When the NULL value has already been set
Even if you press NULL and enable the NULL feature, the NULL value is not updated. The saved NULL
value discussed above is used to correct the measurement function values.
For example, if you turn on the power and then immediately enable the NULL feature, the NULL value has
not yet been set, so the value measured then is used as the NULL value. If you press NULL again afterwards,
the NULL feature is disabled. The WT1800 saves the NULL value. Even if you press NULL and enable the
NULL feature, the NULL value is not updated. The saved NULL value discussed above is used to correct the
measurement function values.
• OFF:
Even if you press NULL, the NULL feature is not enabled. Measurement function values are
produced with no NULL correction.
The held NULL value is cleared under the following circumstances.
• Operations that cause the NULL values of all inputs to be cleared
• Turning on the power (the NULL values are not backed up when you turn off the power)
• Initializing the settings
• Loading a setup data file
• Operations that cause the NULL value of the input whose settings were changed to be cleared
• Switching between direct current input and external current sensor input
• Changing the Sense Type setting for the Speed or Torque motor evaluation input signal
NULL Values
When you enable the NULL feature, the following measurement values are used as the NULL values.
• Udc and Idc (the voltage and current simple averages)
• Speed and Torque signals (on models with the motor evaluation option)
• Aux1 and Aux2 (on models with the auxiliary input option)
Measurement Functions Affected by the NULL Feature
All measurement functions are affected by the NULL values.
• If there are no previously measured values for Udc, Idc, Speed, Torque, Aux1, or Aux2, because for
example the NULL feature has been turned on before any measurements have been made, the NULL
values are set to zero.
• For measurement functions that are computed based on an element’s voltage and current values, the
NULL values are subtracted from the sampled voltage and current values.
• For motor evaluation measurement functions and auxiliary input measurement functions, the NULL values
are subtracted from the computed numeric data.
