VXI VT1433B - Manual (Page 132)

Tachometer Description
A tachometer input can be included with the VT1433B 8-Channel 196 kSamples/s
Digitizer plus DSP as VT1433B-AYF. (It cannot be installed with an Arbitrary
Source Option, VT1433B-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
A VT1433B 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 VT1433B 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 VT1433B
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 VT1433B 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.
VT1433B User's Guide
The Tachometer Option
7-2