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Tachometer Description
A tachometer input can be included with the HP E1433A 8-Channel 196
kSa/sec Digitizer plus DSP as Option AYF. (It cannot be installed with a
Source, Option 1D4.) The Tachometer Option is a two channel tachometer
input used to capture the contents of a freerun counter whenever an
external input crosses a programmable threshold.
Tachometer Inputs
The tachometer has two inputs which connect to analog conditioning,
holdoff, and FIFO circuitry. See the block diagram in this chapter. The
inputs can be configured so that one input connector (Tach 2) becomes an
external trigger input and the other (Tach 1) remains a tachometer input.
(The Tach 1 connector cannot be a trigger input.) The switch that
determines this configuration is controlled by software.
External Trigger Input
An HP E1433A without a tachometer option can accept a TTL external
trigger signal (see “Trigger Lines” in the chapter titled “Module
Description”). With the tachometer option the HP E1433A still has that
capability and is also able to accept an analog external trigger signal at the
Tach 2 input.
Trigger Level
The trigger level of the tachometer can be set by software.
Tachometer Monitoring
The tachometer is capable of sending its analog input signal onto the HP
E1433A module’s internal calibration line. The calibration line can be
connected to the 196 kHz 4-channel input assembly, so that the signal on
the tachometer’s connector can be monitored via an input channel. This
can be useful when deciding where to set the trigger level of the
tachometer. An example program is supplied with the HP E1433A Host
Interface library, which shows how to perform this tachometer monitoring.
Exact RPM Triggering
The tachometer can be used to create exact RPM triggering, controlled by
software. The RPM of the tach channel is calculated from tach transition
times. Then the sample numbers in the data FIFO are determined for
exact RPM triggering.
HP E1433A User's Guide
The Tachometer Option
7-2