Buffered Digital Output for Isolated or High-Voltage Applications

This tutorial helps you configure and program NI 653x high-speed digital devices for clocked (or buffered) digital output applications that require voltage isolation or generation of signals with voltage levels that exceed TTL-compatible voltages.

For applications involving field digital logic levels, such as TTL and CMOS, where high common-mode voltages can be present, you can use the SCXI 1163 isolated output module. Use the 653x device with the SCXI-1163R modules to switch high-voltage loads, up to 240 VAC/VDC and up to 200 mA. The isolation of the SCXI-1163 and SCXI-1163R modules eliminate ground-loops and isolate the host computer from damaging voltages.

The voltage levels required by your application determine which module you need.

• SCXI-1163 -- for isolated digital output up to 5 V +/- 0.5 V
• SCXI-1163R -- for isolated digital output of 5 to 240 VDC/VAC

Required Hardware

• NI 653x device
• SH68-68-D1 cable
• SCXI chassis
• SCXI-1355
• SCXI-1163 or SCXI-1163R
• SCXI-1326

  Hardware Overview
  

The NI 653x devices include the NI PCI-6534, NI PXI-6534, NI PCI-DIO-32HS, NI PXI-6533, NI DAQCard-6533, and the NI AT-DIO-32HS. All these devices work equally well in this application.

The SH68-68-D1 is a shielded, series-terminated, twisted-pair cable, which is well suited for high-speed digital applications.

Signal Conditioning eXtensions for Instrumentation (SCXI) is a versatile, high performance signal conditioning platform. The SCXI chassis is made to house, power, and control SCXI modules and conditioned signals.

The SCXI-1355 is a cable assembly used to connect the back of an SCXI-1163 or SCXI-1162 module to the SH68-68-D1 cable.

The SCXI-1163 and the SCXI-1163R are 32-channel isolated digital output modules.

• The SCXI-1163 is for 5 V TTL or CMOS output signals that need up to 240 V of isolation from the computer’s ground to eliminate ground-loop problems and protect the host computer.
• The SCXI-1163R offers Solid State Relay isolation for signals up to 240 VDC/VAC up to 200 mA.
  

The SCXI-1326 is a high-voltage terminal block that mounts to the front of an SCXI-1163 or SCXI-1162 module.

To perform high-voltage clocked/buffered digital output, configure the SCXI input module for parallel mode in conjunction with the NI 653x device. In parallel mode, the SCXI module can bypass the SCXI backplane, so all 32 lines are always accessible. In multiplexed mode, the SCXI backplane multiplexes the 32 lines to one serial line.

Notice that in multiplexed mode all modules in an SCXI chassis can be multiplexed to one module and to one NI 653x. In parallel mode, each parallel-mode module has a dedicated connection to one NI 653x.

Installing and Configuring Your Hardware

Step 1. Install your NI 653x
Before installing your NI 653x, ensure that you have installed the latest version of NI-DAQ. NI-DAQ is the driver software that controls National Instruments data acquisition (DAQ) hardware. Configure the NI 653x in Measurement & Automation Explorer (MAX). For more information on installing and configuring a DAQ device, refer to the Hardware Installation Wizard at http://www.ni.com/support/install/

Step 2. Set SCXI Module Jumpers
Before installing your SCXI-1163/1163R in the SCXI chassis, set the jumpers to the settings shown below. Table 1 lists the jumper settings for the SCXI-1163; use the following figure to locate the jumpers on the SCXI-1163. Table 2 lists the jumper settings for the SCXI-1163R.

• SCXI-1163

• SCXI-1163R
Table 2. SCXI-1163R Jumper Settings

Jumper	Setting	Description
W1	N/C	--
W2	D	DIO
W3	D	DIO
W4	A	Pull up resistor
W5	PAR	Parallel Connection
W6	P	Parallel Connection

Step 3. Assemble the System
Connect the components of your system as shown in the following figure, according the following procedure:

1. Insert the SCXI-1163 or SCXI-1163R module into an unused slot in the SCXI chassis.
2. Connect the SCXI-1355 shielded cable assembly (which includes the SH6868-D1 cable) to the back of the SCXI-1163/1163R module.
3. Connect the SH68-68-D1 cable to the NI 653x in the computer and to the SCXI-1326.

Step 4. Connect Signals to the SCXI-1326 Connector Block

Tip: It is easier to make connections to the SCXI-1326 connector block while it is not connected to the front of the SCXI-1163/1163R.

The SCX1-1326 signal connections are shown in the following figure.

• SCXI-1163
  Connect the desired output voltage between V_CC and GND. The outputs are connected from CHAN(n) to GND.

• SCXI-1163R
  The following figure illustrates the switch connections for the eight banks of output lines on the SCXI-1163R. Depending on the logic level of the 653x line, the corresponding line is shorted to GND or open.
  

Notice that there are eight different terminals with four outputs each. The V_CC and/or GND must be connected to each bank for that bank's four outputs to work. You can connect different voltage sources to different banks, if you need to operate individual banks at different voltage levels.

Note: Do not configure the SCXI-1163R in such a way that the voltage difference between any V_CC, GND, or CHAN(x) and any other V_CC or GND or CHAN(x) exceeds 240 Volts.

For more information, refer to the SCXI-1163, SCXI-1163R or SCXI-1326 documentation. Click the links at the bottom of this page to download PDF copies of these manuals.

Step 5. Configure Your System in MAX

Double click the Measurement & Automation icon on your desktop to launch MAX, then configure your SCXI module as shown in the following procedure.

a. Right-click Devices and Interfaces and select Create New.

b. Select the SCXI chassis you are using, then click Finish.

c. Set Auto-Detect modules to No, as shown in the following figure. Click Finish.

d. Expand the SCXI Chassis folder in MAX to display all of the available module slots. Right-click the slot your SCXI module is in, and select Insert... from the menu.

e. Locate your SCXI module in the list, click it to select it. Click Next to continue.

f. Select the NI 653x from the Connected To drop-down list. Deselect This device will control the chassis. Choose parallel mode as the Operating Mode, then click Next.

g. Choose the SCXI-1326 from the Accessory drop-down list, then click Finish to complete the configuration of your system in MAX.

For more information about installing and configuring SCXI systems, refer to the SCXI Installation Wizard at http://www.ni.com/support/scxi/

Transfer Rates

The propagation delay of the SCXI-1163 is 100 ns and the risetime is 1 µs. You can calculate the maximum update rate of the system by using the following formula:Where propagation delay is the larger of the risetime, turn-on time, and turn-off time.

Using this formula for the SCXI-1163 you get the following result for your maximum update rate:
Note: You can add pull-up resistors to obtain faster rise times; however, adding pull-up resistors increases the current required to drive the output.

The SCXI-1163R has a power-on time of 1.5 ms and a power-off time of 0.25 ms. The formula gives us a maximum update rate of 667 Hz, as shown below.
Because the NI 6534 and the NI 6533 have update rates higher than 1 MHz, which is faster than the SCXI-1163/1163HV, the propagation delay of the SCXI-1163/1163HV is the limiting factor.

Software Examples

Use the Buffered Pattern Output.vi or Cont Pattern Output.vi examples from LabVIEW. Buffered Pattern Output.vi outputs the specified pattern one time and then stops. Cont Pattern Output.vi outputs a pattern until the VI is stopped. For more information on these LabVIEW examples, please see the LabVIEW example documentation.

Other System Considerations

1. It is possible to have SCXI modules configured for both parallel and multiplexed modes within the same SCXI chassis. For example, you can have one module in parallel mode connected to its dedicated DAQ device and the rest of the modules in the same chassis can be multiplexed to a separate DAQ device.

2. To do both input and output on the same host computer, you must use two 653x devices, each in parallel mode, with the respective input and output SCXI modules. For more information about digital input with SCXI signal conditioning, click the link for Buffered Digital Input for Isolated or High Voltage Applications below.
Related Links:
653X User Manual
SCXI-1163 Manual
SCXI-1163R Manual
SCXI-1326 Manual
Buffered Digital Input for Isolated or High-Voltage Applications

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