Vanguard LTCA-10_40 - Manual (Page 57)

LTCA-10/LTCA-40 USER’S MANUAL
57
6.0 LTCA-10/40 SPECIAL FEATURES
6.1 Bypassing the Resistance Value Display Delay
When the LTCA-10/40 first applies the test voltage to the transformers winding, the current is
increased slowly until the transformer’s winding reaches saturation. During this period, the
resistance value varies substantially and the readings may appear unstable to the operator. The
LTCA-10/40 has a built-in 3 minute minimum delay between the start of the test and when the
resistance value is displayed on the LCD. This feature eliminates the possibility of early
erroneous readings. Depending on the transformer size, the delay may be longer than 3 minutes.
The operator can bypass this delay and observe the test results immediately. To bypass this
delay, press the
[9]
key, the
[8]
key, and the
[7]
key from the “START-UP” menu. The LTCA-
10/40 will then begin displaying resistance values as soon as measurements are made. This
bypass setting will remain active until the unit is turned off. When the unit is turned on again, it
will use the default 3 minute minimum delay before displaying resistance values.
6.2 Converting Resistance Measurements
The LTCA-10/40 can convert the resistance reading of the device under test at its present
temperature to the equivalent resistance value at a different temperature. The conversion is
accomplished by the following formula:
Rs = Rm (Ts + Tk) / (Tm + Tk)
Where:
Rs is the resistance at desired temperature
Rm is the measured resistance
Ts is the desired reference temperature
Tm is the temperature at which the resistance was measured
Tk is the constant used for the winding material
Tk = 234.5 for copper
Tk = 240.0 for aluminum