Logos Electromechanical
5
© 2010 Logos Electromechanical CC-BY-NC-ND 3.0
The two resistors included with the kit are both 1% metal film resistors with a
temperature coefficient of 50 ppm/°C. The 182Ω resistor corresponds to a gain of 333
and the 121Ω resistor corresponds to a gain of 500. If the 10V excitation is selected,
these produce a 5V full scale output from a 3mV/V or 2 mV/V full-scale sensor,
respectively. These are common full range values for load cells and pressure
transducers. No gain resistor is installed by default; either select the appropriate one
from the two provided or acquire an appropriate one for your application.
Selecting Excitation
The INA125 provides four excitation modes. In addition, the default excitation modes
can be augmented with external circuitry. The default modes are 10V, 5V, 2.5V, or 1.24V
(BG). The appropriate voltage is selected by making one of the four provided solder
jumpers. These are on the output side of the board next to the end of the INA125, and
are labeled J-10, J-5, J-2.5, and J-BG. Never make more than one at a time. They are left
unmade by default in order to ease customization by the end user.
Selecting Reference
Since the INA125 is factory trimmed for extremely low offset and drift. Therefore, no
offset adjustment will be required for most applications. When no offset is desired, the
Vref pin should be shorted to ground. A solder jumper, J-REF, (unmade by default) is
provided for this purpose. When an offset is desired, it is set by providing a voltage to
this pin. The voltage on this pin is added to the output signal. It is imperative that the
value provided to this pin not be outside of the range of internal power supply rails (i.e.
greater than +11.5V or less than -5.75V). A low impedance voltage source is desirable in
order to provide good common-mode rejection.
Trimming the Board (optional)
If you wish to use the board in a compact space, like the aforementioned Bulgin
Ethernet Buccaneer, you will need to trim off the ends. This can readily be accomplished
