Input Signal Conditioning - Racal Instruments 2251A Operator's Manual

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Input Signal Conditioning

1.3.1 The following signal conditioning capabilities are available to both inputs A and B
independently.
1.3.1.1 AC or DC coupling
1.3.1.2 1 Megohm or 50 ohm input impedances
1.3.1.3 X1 or X10 input attenuations
1.3.1.4 Positive or negative slope triggering conditions
1.3.1.5 Automatic or user defined input trigger level setting. Note the use of the auto-trigger facility
may cause the 2251A input attenuator to change between X10 and X1.
1.3.1.6 Low Pass Filter. A switchable low pass filter is provided that reduces the bandwidth of input
A to 50 kHz (nominal).
1.3.2 Additional Capabilities
1.3.2.1 External Arming. Additional qualification of the trigger conditions of a measurement is
provided by input D or the VXI trigger bus. Arming conditions are selected by the use of
special functions available in the command set.
1.3.2.2 External Frequency Standard Input. The 2251A may be locked to an external reference
frequency applied to this input. Selection of the reference frequency is under software
control.
1.3.2.3 Math Function. When the math function is active, the 2251A returns values of the form [
(Result - X) Y / Z ] where Result is a measured value, and X,Y and Z are constants entered
by the operator.
1.3.2.4 Averaging Mode. An additional digit of resolution is added to the 2251A output string in this
mode. Averages 100 measurements.
1.3.2.5 Special Functions. The measurement and diagnostic capabilities of the
2251A are extended by the special functions available in the command set.
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