NetDAQ
Service Manual
2-60
Table 2-21. Frequency Sensitivity
Measured Amplitude
Range Used for Frequency Measurement
Less than 3V
ACR1 (300 mV)
Between 3V and 30V
ACR2 (3V)
Greater than 30V (2640A only)
ACR3 (30V)
The frequency measurement itself does not use the A/D. Frequency measurements are
taken using the Stallion chip. To reduce noise in frequency measurements, the
instrument takes eight frequency readings and averages them together to obtain a single
frequency measurement.
There is only one frequency range (this is different from sensitivity), and therefore the
range field of the channel configuration is ignored for a frequency channel.
The only difference between the three measurement rates for a frequency reading is the
length of time allowed for settling. See Table 2-18: Signal Conditioning Settling Time.
If the status bits returned by Stallion indicate a low frequency (PEROVER bit set), a
value of 0 Hz is returned. If they indicate a high frequency (PEROVER bit clear and
FREQOVER bit set), a value of PLUS_OVLD_VAL (defined in Perform Scan) is
returned.
If the FRDY interrupt is not received within 500 ms of starting a frequency
measurement, the input signal is assumed to be too low in amplitude or frequency to
measure, and a value of 0 Hz is returned.
VAC Discharge Mode
2-111.
After a frequency or VAC reading, the hardware is configured to discharge certain signal
conditioning capacitors, charged during the measurement. This is done to avoid
disturbing the measurement of a subsequent VAC or frequency measurement. The
function relays are set to the VAC discharge position, as given in Table 2-15: Function
Relays, and the DISCHARGE signal is set high. After 6 ms, the DISCHARGE signal is
once again set low.
Autoranging
2-112.
The configuration of each channel includes the state of autoranging for that channel,
either enabled or disabled. When performing a measurement on a channel that has
autoranging enabled, the instrument first attempts a measurement on the range that was
used on that channel for the previous scan. If this results in an overrange or underrange,
the instrument up-ranges or down-ranges accordingly. Channels that are configured with
autorange enabled, but have not yet been measured start on the highest legal range for
the channel’s function type.
Autoranging may decrease the measurement rate, since readings on multiple ranges may
be required for a single channel. On the slow and medium rates, only the first A/D
reading of a measurement is used to determine whether a range change is required.
Содержание NetDAQ 2640A
Страница 14: ...NetDAQ Service Manual x...
Страница 46: ...NetDAQ Service Manual 2 4...
Страница 106: ...NetDAQ Service Manual 2 64...
Страница 108: ...NetDAQ Service Manual 3 2...
Страница 164: ...NetDAQ Service Manual 4 42...
Страница 206: ...NetDAQ Service Manual 6 2...
Страница 218: ...NetDAQ Service Manual 6 14 2645A 1601 Figure 6 2 A1 Main PCA Assembly...
Страница 220: ...NetDAQ Service Manual 6 16 2620A 1601 Figure 6 3 A2 Display PCA Assembly...
Страница 225: ...List of Replaceable Parts Parts Lists 6 6 21 2640A 1603 Figure 6 4 2640A A3 A D Converter PCA Assembly...
Страница 230: ...NetDAQ Service Manual 6 26 2645A 1603 Figure 6 5 2645A A3 A D Converter PCA Assembly...
Страница 234: ...NetDAQ Service Manual 7 2...
Страница 242: ...2640A 2645A Service Manual 7 10 Figure 7 2 A2 Display PCA Assembly 2620A 1602...
Страница 243: ...Schematic Diagrams 7 7 11 Figure 7 2 A2 Display PCA Assembly cont 2620A 1002...
Страница 244: ...2640A 2645A Service Manual 7 12 2640A 1603 Figure 7 3 2640A A3 A D Converter PCA Assembly 2640A 1603...
Страница 251: ...Schematic Diagrams 7 7 19 2645A 1603 Figure 7 4 2645A A3 A D Converter PCA Assembly 2645A 1603...
Страница 258: ...2640A 2645A Service Manual 7 26 Figure 7 5 A4 Analog Input PCA Assembly 2620A 1604...
Страница 260: ...2640A 2645A Service Manual 7 28...