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Re vision:
User's Manual (MUT)
N1145 Quad Scaler and Preset Counter/Timer
05/11/2003
0
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00115/01:N1145.MUTx/00
N1145_REV0.doc
14
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with the TIMER switch:
(
τ
=1
µ
s or 1 ms)
•
select a value N (for instance a power of 10) with the thumb wheel switches. The
measurement time is then: Ti=N
τ
•
use the OUT signal as the GATE input to the selected
section 1 to 4
Counter(s),
operating in GATE+CLEAR mode.
The external input frequency is then given by:
ƒ
i=(Mc)
/
(N
τ
)
where Mc is the number of pulses received by the Counter while GATE is active.
4.4. Divider
Section 5
can also be used as a divider of an external input sequence. For that purpose:
•
connect the END MARKER output to the LOAD input.
•
Select the input / output ratio R by setting the thumb wheel switches.
•
Connect the external input at the
section 5
input port and pick the NIM output from the
OUT ports, which is a pulse generated every R pulses at the input.
4.5. Delay unit
Section 5
can also be used to generate a delayed pulse (at the END MARKER output) or
transition (at the OUT ports).
An absolute delay can be obtained with section 5 in TIMER Mode. The duration of the
delay is Td=N
τ
(actually the time interval between the LOAD signal leading edge and the
leading edge of the END MARKER) where N is the preset value on the Thumb wheel
switch display, and
τ
is the internal clock period. The time delay is the elapsed time
between the time of the leading edge at the LOAD input and leading edge either at the
END MARKER output. See the next section for accuracy. With the counter in COUNTER
Mode, a relative delay (in terms of number of pulses) can be obtained between the
NIM/TTL input and the END MARKER, after the preset number of input pulses have been
counted.
4.6. Measurement accuracy
For the previous applications, it is important to remember that with any measurement
made with a counter on a periodic waveform there is always an intrinsic uncertainty of
one pulse. This is due to the fact that, depending on the position of the start of the
measurement window with respect to the period of the waveform, one pulse may or may
not be totally included, and thus counted for. This also applies to the uncertainty of the
selection of the reference time window.
