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Number 2266
Application Note System Tests With the KPCI-3130 Series
Series Analog Output Card
The load will be connected to the analog output in 2-wire
Introduction mode as shown in Figure 1 and then connected in 4-wire mode
Today, the electronics community is experiencing a migration using the sense line inputs as shown in Figure 2. The OUT0 and
away from traditional test and measurement philosophies and GND signals will be connected to pins 1 and 19 respectively, and
encompassing a more hybrid approach. Several years ago, if one the S0H and S0L signals will be connected to pins 2 and 20.
were required to generate or to measure very precise data points,
few solutions were available other than benchtop instrumenta- Analog
tion. However, the continued evolution of electronic components
has lead to the fabrication of precise voltage sources and high- OUT0
resolution A/D (analog/digital) and D/A hardware, creating a
variety of new solutions. Analog
Output DUT
The ability to generate instrument quality analog voltages
is available in the KPCI-3130 Series analog output boards. The
KPCI-3130 is designed to the PCI-bus standard and provides a Return
wide feature set that is typically not seen in PC-based plug-in
analog output hardware. Two of the most unique characteristics GND
of the board are the 4-wire remote sense feature and the
4-quadrant source/sink operation. The functionality of these Figure 1. Conventional 2-Wire Analog Output Connections
features is illustrated in the following test examples.
4-Wire Remote Sense Test Description Analog
The ability to perform 4-wire remote sense operations provides a OUT0
significant advantage over standard analog output hardware. This Sense HI
feature becomes of critical importance when generating control
signals over long distances. Significant voltage drops can occur S0H
Analog
as the result of cable resistances, device interconnections, and DUT
Output
terminations; therefore, the programmed output value may not be Adjust Vsource
Sense LO
the voltage delivered to the device under test (DUT). (Feedback)
S0L
Incorporating 4-wire remote sense functionality provides
the ability to connect sense leads directly to the input of the Return
DUT. The sense high and low connections allow the card to mea-
GND
sure (sense) the actual voltage present at the DUT. The analog
output can then be automatically adjusted, transparently to the
user, to ensure that the required voltage is supplied, regardless of Figure 2. Analog Output with 4-Wire Remote Sense
cable lengths and interconnection losses.
The data below was obtained using the KPCI-3130's
4-Wire Remote Sense Test Procedure source feature and a Model 2700 Multimeter/Data Acquisition
System:
In this test, a known voltage level will be programmed from the
KPCI-3130 and connected to the DUT using several different Resistance Programmed 2-Wire Mode 4-Wire Mode
cable lengths. The output voltage will be programmed with Signal Path (Ohms Value Measured Value Measured Value
(Per lead) Per lead) (Volts) (Volts w/o sense) (Volts w/sense)
ExceLINXTM (Keithley's Excel add-in), and the resistance of the
cable will be measured using a Keithley Model 2700 Multimeter/ 10 ft cable 0.5266 8.000 7.999 8.000
Data Acquisition System that is set to 4-wire ohms mode. For 100 ft cable 2.5 8.000 7.920 8.000
comparison purposes, the voltage at the DUT will also be meas- 6 relays, 4
ured without remote sense (this is typically referred to as interconnections, 4.06 8.000 7.360 8.000
2-wire mode). 20 ft cable
The data clearly indicates that cabling and device intercon- The analog output voltage will now be a function of the
nections can be significant sources of error. voltage programmed, and sensed, across the shunt resistor. The
acceptable shunt voltage levels can once again be determined
using Ohm's Law and the specified current:
Constant Current Source Vmaxshunt = 20mA