Ectron 441A, Инструкция по эксплуатации, Страница: 33 / 74

Similarly, the voltage set points determine the output voltages corresponding to the upper-
and lower-frequency set points, respectively. The voltage set points can be any voltage from
−
10 V to
+
10 V with a resolution of 0.1 V. The two voltage set points can be within 0.1 V.
Table 4-1 illustrates converter operation with hypothetical frequency and voltage set points.
Table 4-1
Input Frequency vs Output Voltage (Example)
Frequency set points Voltage set points
Upper
(
f
U
)
Lower
(
f
L
)
2000 Hz
1000 Hz
Upper
(
V
U
)
Lower
(
V
L
)
+ 5 V
0
V
Input Frequency Output Voltage Input Frequency Output Voltage
1000 0 3500
+
10.5*
1500 + 2.5 900 − 0.5
2000 + 5 500 − 2.5
3000 + 10 0 − 5
* The output limits at approximately ± 11 V.
Should the application require it, the output can be set to provide a bipolar output (e.g., for
a certain frequency range the output can be set to go from
−
5.000 V to
+
5.000 V). Similarly,
the output voltage could be set to be all negative. Note that the higher frequency will always
produce the more positive output voltage.
Because the minimum difference between the upper- and lower-frequency settings is 10 Hz,
and the minimum difference between the upper- and lower-voltage settings is 0.1 V, it is
possible to set f
U
at 1000 Hz and f
L
at 990 Hz, V
U
to 1.0 V and V
L
= 0.9 V, thus giving a
frequency-to-voltage sensitivity of 100 Hz/V. Exactly the same results would be obtained if
the settings were f
U
= 1500 Hz, f
L
= 900 Hz, V
U
= 6 V, and V
L
= 0 V. The following section
shows that extreme settings can result in poor resolution and noise.
NOISE
In addition to frequency jitter of the input signal, noise at the output of the Model 441A
will be a combination of input signal noise, waveform character, signal amplitude, and in-
strument settings. For square and pulse waveforms, output noise should be well under the
10 mV p-p specification assuming sharp rise times and good pulse-to-pulse frequency and
phase stability. Ideally, rise times should be under 5
µ
s to utilize the extraordinary conversion
accuracy, resolution, and stability of this instrument. A further source of noise can be ground-
ing problems of input and output signal circuits.
Despite the fact that the amplifier’s input is differential, input-to-output cross talk can exist
external to the amplifier. Good wiring practices should be followed to minimize this effect
(see Page 4-1, INPUT SIGNAL GROUNDING AND SHIELDING).
An additional source of input-to-output crosstalk is an inadequate case ground. All pins of
the connector incorporate emf-rfi filters. The capacitors associated with these filters connect
to case ground (Pin 5 on the DA connector). Consequently, if no case ground exists, signals
from one pin will be coupled to other pins by these capacitors. For example, if a sharp-rise
Model 441A Applications
4-3