Omega Engineering OMB-DBK-34A, User Manual

Page: 174 / 250

The user-supplied excitation source should provide adequate current levels for all the DBK16s that are
powered. The minimum current required for the user-supplied excitation source for each transducer
(2 per DBK16) is:
I
MIN
= Excitation voltage/R + 5 mA (where R = the resistance of 1 element in the bridge
circuit)
The user-supplied excitation source must be 12 to 15 VDC and connected with the proper polarity.
Enhanced DBK16 cards contain two additional jumpers (JP6 and JP7). Their configuration determines
whether the channel excitation regulator’s power source is
external (default) or internal . Review the
following note and CAUTION prior to selecting the internal power source .
ƒ
JP6 – Selects the upper channel’s source. Default is external.
ƒ
JP7 – Selects the lower channel’s source. Default is external.
It is possible to power excitation regulators from an in15 V on the LogBook’s
or Daq device’s P1 if no other DBKs are being used. On enhanced DBK16 cards, two
3-pin headers (JP6 for upper channel and JP7 for lower channel) are set by default to
use an external power source. Moving the jumpers to the internal position connects the
excitation terminals to the +15 VDC rail from P1.
CAUTION
Avoid overloading LogBook’s , DaqBook’s or DaqBoard’s +15 VDC power supply. The
power supply can be overloaded if DBK16 jumpers JP6 and/or JP7 are set to “Internal”
and one or more of the following conditions exist:
ƒ
Additional DBKs are being used.
ƒ
120
Ω
bridge-completion resistors are being used in the strain gage
configuration.
Card Configuration
Factory Defaults:
•
Bridge configuration – Full
•
Coupling – DC
•
Excitation source – External
•
Low pass filter – Disabled (by-passed)
The cutoff frequency, if enabled, has a default of 3.7 Hz. This is obtained using 100k
Ω
resistors for R17, R18, and R19 for the lower channel; and using 100k
Ω
resistors for R5,
R6, and R7 for the upper channel. See the following board layout for resistor locations.
The next few sections of this document module explain the following aspects of configuring DBK16.
•
AC Coupling and Low-Pass Filter Options
•
Channel and Card Address Selection
DBK16, pg. 6
879895
DBK Option Cards and Modules