(d) Slide switch S8 is located on the rear panel of the 1600A. When set
to OFF position, the front panel RESET pushbutton initiates switch to AC mode.
When S8 is set to ON, the reset from DC to AC is automatically recycled
approximately 30 seconds after transfer from AC to DC mode.
This continuous
recycle adds an auto-zero feature to the auto balance mode which avoids transfer
errors caused by long-term thermal variations.
(e) It is recommended that AUTO mode is always used with switch S8 in
auto-zero recycle mode.
(7) Attenuator heating.
When measuring voltages between 250 and 1000
volts, the power dissipated by the input attenuators will produce a slight change
in resistance.
It is recommended that the MANUAL TRANSFER mode be employed when
measuring such voltages and that transfer be made after the signal under
measurement has been applied for approximately two minutes (allowing the input
attenuator resistance to stabilize).
(8) Repeatability. Lack of perfect repeatability is due to internal noise,
finite digital memory resolution, contact resistance in switches and relays,
thermal effects on attenuators, etc.
Since these error sources are random in
nature, several measurements should be made and the results averaged to obtain
ultimate accuracy.
f. The ATS has three modes of operation, each selected by the setting of the
front panel switch.
When the switch is set to MANUAL BALANCE, the operator
manually adjusts the MANUAL BALANCE COARSE and/or FINE controls until a null (O on
the meter BAL scale) is attained.
After transfer, the voltage at the DC OUTPUT
binding posts will be equal to the RMS value of the applied AC signal. While this
mode of operation provides the greatest measurement accuracy (due to the finite
resolution of the digital memory circuitry in the AUTO mode), it is slightly more
time consuming although substantially faster than conventional AC-DC transfer
standard measurements.
When the mode switch is set to AUTO or MANUAL or MANUAL
TRANSFER, the ATS balances automatically. In the AUTO mode, AC to DC transfer is
performed automatically, while in the MANUAL TRANSFER mode the AC to DC transfer
point is determined by the operator. Manual transfer mode is used for moderately
unstable input signals.
g. The ATS can be employed as a voltmeter to provide a relatively coarse
indication of applied signal levels. When the instrument is operated in either the
automatic or manual transfer mode, the DC equivalent of the applied AC signal RMS
level can be read by multiplying the meter DC OUTPUT VOLTAGE scale indication by
the factor specified on the TIMES METER READING dial after transfer has been
achieved.
The voltage thus obtained will be within 5 percent of the true RMS
level of the input signal.
h. An overload protection capability is provided which will automatically
remove the applied signal from the attenuator/thermoelement circuitry whenever
the peak value of the applied signal exceeds 175 percent of the selected
range high voltage peak.
So, if the RANGE VOLTS switch is set to 125 to 250
and the peak value of the applied signal is in excess of 437 volts
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