Chapter 3
NI 4350 Operation
©
National Instruments Corporation
3-11
temperature) and at the cold-junction on the accessory will introduce
error.
To minimize thermal EMFs, use wires of the same thermocouple
type when extending the length of the thermocouple. Also, minimize
temperature gradients in the space enclosing the thermocouple, the
NI 4350 instrument, and its accessories.
Measuring DC Voltage
Connecting Your DC Voltage Signal
The NI 4350 accessories—the CB-27T and CB-27 for the NI 4350
(PCMCIA), and the TBX-68T and TBX-68 for the NI 4350 (ISA) and
the NI 4350 (USB)—are designed to be used with any DC voltage
signal. Consult your accessory installation guide for instructions on
how to connect your voltage signals.
The NI 4350 analog inputs are protected against damage from voltages
within ±42 VDC in all ranges when powered up and ±17 VDC when the
NI 4350 instrument is powered down. You should never apply voltages
above these levels to the inputs.
Caution:
To prevent possible safety hazards, the maximum voltage between any of
the analog inputs and the computer ground should never exceed ±42 VDC
when the NI 4350 instrument is powered up and ±17 VDC when the
NI 4350 instrument is powered down.
Input Ranges
Your NI 4350 instrument has six bipolar input ranges available for
measuring DC voltage. These ranges are ±625 mV, ±1.25 V, ±2.5 V,
±3.75 V,
±
7.5 V, and ±15 V. The NI 4350 instrument can measure DC
voltage to the specified accuracy as long as the voltage is within the
selected input range. To get the best resolution, noise rejection, and
accuracy, choose the smallest possible range. Make sure that each
signal input to CH+ and CH– is within the input common mode limits
of this input range. The input common mode limits are ±2.5 V and
±15 V for the lower three and higher three input ranges, respectively.
!
