a. A positive action peak-sensing overload system that does not clip the
input signal is incorporated in the ATS. This feature eliminates the possibility
of erroneous measurements due to undetected clipping or shunting of the applied
signal.
A nonlocking pushbutton switch is provided to permit removal of the
overload protection capability when measuring signals having a crest factor greater
than 2:1 and to optimize accuracy when measuring signals above 100 kHz.
b. A 12-position range selector switch, in conjunction with the internal
attenuators, enables the measurement of input voltage levels from 0.25 to 1000
volts.
Since the thermoelement has a square-law response, the range selection
technique employed ensures that the equipment will not balance when the
thermoelement driving current falls below approximately one-half the rated level of
5 mA.
This design consideration assures good signal-to-noise ratios for all
measurements.
A 13th switch position provides selection of external remote range
programming.
c. When ATS is operating in the automatic transfer mode, special circuitry
prevents automatic transfer until the thermoelement EMF output rate of change is
0.002 percent/second or less.
This ensures against inaccurate measurements
resulting from the thermoelement not having reached equilibrium. A normal transfer
is accomplished typically in 10 seconds; however, when there is a large change in
heater current, the time required for the thermoelement to reach stable balance is
extended, resulting in a somewhat longer measurement time.
When the ATS is
operated in the manual transfer mode, the instant of transfer is manually
determined. In manually balanced operation, the operator adjusts the level of the
internal balancing voltage until a null indication is obtained and then achieves
transfer by manual switching.
d. The controls, connectors, and indicators required for operation of the ATS
are illustrated in Figure 3-3 and their functions are described in Table 3-1.
Carefully study both to thoroughly familiarize yourself with the instrument before
proceeding. The ATS is a relatively simple instrument to operate; however, there
are a number of "tips" and precautions to become familiar with. Some of these are
similar to those discussed in Lesson 2 for the Model 540B, while others are unique
to the ATS.
(1) If the voltage range of the applied signal is known, the operator need
only set the RANGE VOLTS switch to the appropriate position and couple the voltage
to be measured to either the AC INPUT 0.25V or AC INPUT 32-1000V connector, as
required.
(2) Should the signal be of unknown level, employ the conventional
(500 to 1000) and couple the signal to be measured to the AC INPUT 32-1000V
connector.
If balance cannot be achieved, the operator should increase the
sensitivity of the ATS, switching input connectors when required, until a balance
is achieved.
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