National Instruments SC-2040 - Manual (Page 33)

Chapter 3 Signal Connections
© National Instruments Corporation 3-11 SC-2040 User Manual
where V +
i n
is the signal at the positive input (IN0+ through IN7+), and V -
i n
is the signal at the
corresponding negative input (IN0- through IN7-). Both V +
i n
and V -
i n
are measured with respect
to the SC-2040 chassis ground.
Digital Signal Inputs
If you are using an external trigger, connect the trigger source and the digital reference to screw
connector J9. This signal should be in the range 0 to +5 V, with switching occurring around
1.5 V.
Note: All digital signals on the SC-2040 are referenced to the +5 V power supply. If the
MIO-16E supplies power, it provides this reference. If an external supply provides
power, it provides this reference through connector J13.
A rising edge on the trigger will place the SC-2040 into hold mode, and the SC-2040 will return
to track mode when the MIO-16E indicates that the data acquisition is complete.
Although the TRIG signal is a digital signal, it is still susceptible to noise, particularly at its
transitions. This noise can cause the SC-2040 to enter hold mode on the wrong edge. Two
possible sources of noise are interference and reflection. The best way to reduce noise
corruption is to minimize the distance that the signal must travel. Furthermore, you can
minimize interference by properly shielding the incoming trigger signal. You can minimize
reflection by ensuring that the impedance of the source of the trigger signal matches the
impedance of the cable used to transmit the signal; inserting a small resistor (about 50
Ω
) in
series with the signal source will minimize reflection.
Monitoring Signal Outputs
You can use connector J11 to monitor the signals being sent to and from the MIO-16E board.
Figure 4-3 shows a sampled analog signal as the SC-2040 channel output.
You can also monitor the state of the SC-2040 through line PFI7/STARTSCAN. A high level on
PFI7/STARTSCAN indicates the SC-2040 is in hold mode, while a low level indicates that the
SC-2040 is in track mode.
Other Connection Considerations
Refer to the sections titled Analog Input Signal Connections and Cabling and Field Wiring in
Chapter 3 of your MIO-16E board user manual for additional signal connection information.