Measurement-computing USB-1208FS Bedienungsanleitung PDF herunterladen (Seite 14)

USB-1208FS User's Guide Functional Details

Channel-Gain queue

The channel gain queue feature allows you to set up a scan sequence with a unique per-channel gain setting and

channel sequence. The gain settings are stored in a channel-gain queue list that is written to local memory on

the device.

The channel-gain queue list can contain up to 16 elements in any order. The channel-gain queue list can contain

up to 16 elements in any order. An example of a four-element list is shown in the table below..

Sample channel-gain queue list

Element Channel Range

0 CH0 BIP10V

1 CH0 BIP5V

2 CH7 BIP10V

3 CH2 BIP1V

When a scan begins with the gain queue enabled, the USB-1208FS reads the first element, sets the appropriate

channel number and range, and then acquires a sample. The properties of the next element are then retrieved,

and another sample is acquired. This sequence continues until all elements in the gain queue have been selected.

When the end of the channel list is detected, the sequence returns to the first element in the list. This sequence

repeats until the specified number of samples is acquired.

Carefully match the gain to the expected voltage range on the associated channel or an over range condition

may occur. Although this condition does not damage the device, it does produce a useless full-scale reading,

and can introduce a long recovery time due to saturation of the input channel.

Analog output

You can connect up to two analog output connections to D/A OUT 0 and D/A OUT 1. Each channel can be paced

individually at rates up to 10,000 updates per second. Both channels can be paced simultaneously using the

same time base at 5,000 updates per channel. The 0 V to 4.096 V output range provides a convenient 1 mV per

LSB when setting the output voltage levels.

Digital I/O

The device has 16 digital bits that are configured as two 8-bit ports (Port A and Port B). You can connect up to

eight digital I/O lines to each port (terminals

Port A0 to Port A7 and Port B0 to Port B7). Each port is

configurable as either input or output.

When configured for input, you can use the digital I/O terminals to detect the state of any TTL level input.

Refer to the schematic shown in Figure 8.

Figure 8. Schematic showing switch detection by digital channel Port A0

If you set the switch to the +5V input, DIO0 reads TRUE (1). When set to GND, Port A0 reads FALSE (0).

For more information on digital signal connections

For more information on digital signal connections and digital I/O techniques, refer to the Guide to DAQ Signal

Connections (available on our web site at www.mccdaq.com/signals).

Pull-up/down configuration

Boards designed with hardware revision D and later have user-configurable internal jumpers to configure the

digital bits for pull-up (default) or pull-down. The hardware revision is listed with the part number on the

bottom of the device, for example P/N 193331D.

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Measurement-computing USB-1208FS Bedienungsanleitung Seite 14