Omega Engineering OMB-DBK-34A, User Manual

Page: 144 / 250

The following graph shows typical sine-wave sensitivity in peak-to-peak voltage vs frequency. Six
combinations of attenuation (on/off) and low-pass filtering (30 Hz, 300 Hz, and 100 kHz) are graphed.
Digital Input Signal Conditioning
The equivalent digital input circuit is shown in the figure. The
input signal may range from -15 to +15 V. Higher voltages may
damage the DBK7.
When the input circuit jumpers are set for digital, the outside
(shield) conductor of the BNC connector connects directly to
ground. The center conductor is pulled up with 27 K
Ω
to +5 V
and then passes through a 2.7 K
Ω
protection resistor before being
detected by a Schmitt-trigger buffer with input-protection diodes.
The input thresholds are fixed TTL levels. Below 0.5 V (0.8 V
typical), the Schmitt-trigger buffer output is low. Above 2.1 V (1.6 V
typical), the buffer output is high. The 27 K
Ω
pull-up resistor allows
the digital inputs to sense switches or relays connected directly to the
DBK7 as shown in the figure. The debounce circuit can remove noise
effects of switching.
The input impedance for digital signals depends on the signal level. For signals between 0 and 5 V, the
input-protection diodes do not conduct, and the digital input impedance is just the 27 K
Ω
pull-up
resistance. For signals less than 0 V or greater than 5 V, the input-protection diodes conduct and the
impedance drops to about 2.4 K
Ω
. The figure shows the approximate digital-input current/voltage
relationship.
DBK7, pg. 10
879895
DBK Option Cards and Modules