Measurement Computing DBK Part 2 - Manual (Page 118)

DBK55, pg. 8 988793 DBK Option Cards and Modules
Input Circuit Selection: Analog or Digital
Each input channel can be set for the analog (default) or digital circuit. Two jumpers must be set for each
channel. These are listed in the preceding table, along with the associated channels.
Refer to the previous figure and table; then select the input circuit for each input channel as follows:
1.
Determine the best circuit type for each channel.
•
The digital input circuit works best for DC-coupled signals where the low level is less than
0.5 V and the high level is above 2.5 V and the voltage does not exceed
±15 V. By using a
pull-up resistor, switches and relays can create the signal. Frequencies can be as high as
960 kHz. The digital input circuit does not attenuate or filter the input signal.
•
The analog input circuit is AC-coupled and is sensitive to signals from 100 mV to 84 V p-p.
It also provides attenuation and low-pass filtering to reduce the effects of noise.
2.
Position each channel’s circuit jumpers (2 jumpers per channel) for analog or digital.
3.
Verify that both jumpers for a channel are set the same, i.e., both set to pins 1 and 2 for Analog, or
both set to pins 2 and 3 for Digital.
Attenuation Selection (Analog Input Circuit Only)
When measuring strong analog signals, the attenuator can reduce the input sensitivity and the effects of
noise. If enabled, the attenuator reduces the input sensitivity by a factor of 50.
Refer to the previous figure and table; then set the attenuation for each channel as follows:
1.
Decide whether or not you want attenuation for a given channel. Attenuation enabled, which
reduces sensitivity, is the default setting.
•
Use attenuation (reduced sensitivity) if the input signal’s peak level exceeds 1 V.
•
Disable attenuation (full sensitivity) if the input signal’s peak level is less than 1 V.
2.
For attenuation, position the associated jumper across pins 1 and 2. To disable attenuation (full
sensitivity), position the jumper across pins 2 and 3.
3.
Verify the jumper position for each input channel.
Low-Pass Filter Selection (Analog Input Circuit Only)
The low-pass filter removes high-frequency noise that would otherwise have the DBK55 detecting a higher
frequency than desired. To set the low-pass filter:
1.
Determine the highest frequency you expect to measure on each input channel.
2.
Select the next higher cutoff frequency (30 Hz, 300 Hz, or 100 kHz) for each corresponding channel.
Verify that the DBK55’s sensitivity will accommodate the expected input signal strength. Page 3
includes a graph of typical sine-wave sensitivity (peak-to-peak voltage) verses frequency (Hz).
3.
Refer to the previous figure and table; then set the associated jumpers for the desired low-pass filter
selection.