National Instruments SC-2040 Other Connection Considerations

Chapter 3 Signal Connections

where V+in is the signal at the positive input (IN0+ through IN7+), and V-in is the signal at the

corresponding negative input (IN0- through IN7-). Both V+in and V-in are measured with respect

to the SC-2040 chassis ground.

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.

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.