Unitek Peco 3-131-XX, User Manual

Page: 40 / 49

WELD SENTRY 2 Page 35
GAIN SETTINGS
The voltage and current signals are amplified by a gain factor which is used to convert all signals to a 0 to
10V signal which is required for the Sentry's input circuits. The gain factor is used in measurement
calculations and to set the proper measurement scale for the waveform graphs. The Gain Setting is set
automatically during Basic Setup and is determined by the peak value of the sample weld. A Voltage Gain
and Current Gain are saved as part of the Sentry Schedule. Whenever the voltage or current is greater than
the scale set by the gain “overload” error will occur. The effect of an overload is that the measured value
will not be correct and will be calculated only at the full scale value. The table below lists the Gain Settings
and corresponding Full Scale Measurement values.
FULL SCALE MEASUREMENT
GAIN
SETTING
VOLTAGE (max)
CURRENT (max)
1x Coil
CURRENT (max)
10x Coil
32 312.5mV 312.5 A 31.25 A
16 625mV 625 A 62.5 ^
8 1.25V 1250 A 125 A
4 2.5V 2500 A 250 A
2 5V 5000 A 500 A
1 10V 10000 A 1000 A
0.8 12500 A 1250 A
0.4 25000 A 2500 A
0.2 50000 A 5000 A
0.l 100000 A 100000 A
1.5 20V
0.25 40V
CURRENT / VOLTAGE DIFFERENCE MEASUREMENT MODE (U.S. Pat. No. 5,081,338)
Monitoring conductive welds has always been difficult because the resistance of the tungsten or
molybdenum electrodes is significantly greater than that of the workpieces. Therefore, the weld current
changes very little during the welding sequence. The Sentry uses a Unitek Peco patented solution in which
both the Weld Voltage and Weld Current are amplified to the same level and then the Current is
mathematically subtracted from the Voltage. Since a change in resistance causes the voltage and current
signals to change in opposite direction, the difference between the two becomes an even more sensitive
indication of resistance change. The table below illustrates that the relative change in CURRENT minus
Voltage can be significantly larger than the change in current or voltage.
WELD #1 #2 % CHANGE
AMP
●
SEC 267.1 268.3 + 0.45 %
VOLTS
●
SEC 297.4 294.9 - 0.84 %
WATTS
●
SEC 66.54 66.37 + 0.20 %
OHM
●
SEC 3.257 3.211 - 1.41 %
(KAMPS – VOLT) SEC - 10.17 - 8.87 - 12.18 %