Analog Input

Reads analog inputs of the Q8 data acquisition system.

Library

qctools

Description

The Analog Input Module for the Q8 series of I/O cards provides a mechanism for reading the voltage levels of any analog input on an installed Q8 I/O card. The block can provide a scalar or vector output. The input may either be in units of volts or a raw 14-bit converter values. Analog inputs on the Q8 may range from -10V to +10V.

Parameters and Dialog Box

Board Number

The board number of the I/O card. If there is only one Q8 board in your system, then the board number should be zero. The second Q8 board in your system is board number 1, etc.

Channel(s) to Use

The channel numbers corresponding to each output. For example, if there are 3 outputs, then the entry [4,2,0] assigns output 1 to A/D input 4, output 2 to A/D input 2 and output 3 to A/D input 0. The channel numbers may range from 0 to 7, since there are 8 single-ended A/D channels on the Q8 I/O boards.

Sample Time

A sample time must be specified for all discrete blocks. The default value extracts the sample time from the RTW Options dialog, under Solver/Fixed step size. A numeric value rather than 'auto' should be specified in this dialog field for this default to make sense.

Read After Conversions Complete

Checking this option causes the Q8 driver to read the A/D conversion results from the A/D onboard FIFOs after all A/D conversions are complete. If this option is not checked, then the Q8 driver reads the conversion results as soon as they are available, not waiting the the FIFOs to fill. While it is marginally slower to read after conversions are complete, this option yields slightly better noise performance because it avoids use of the digital logic of the A/D chips while conversions are taking place.

Simultaneous Sampling

When this option is checked, the Q8 driver samples all selected channels simultaneously. The Q8 contains two four-channel simultaneous sampling A/D chips: ADC03 and ADC47. The ADC03 chip handles channels 0-3 and the ADC47 chip handles channels 4-7. Hence, if only one A/D chip is being used, the Q8 always samples simultaneously. If both A/D chips are being used then this option affects whether the two chips are synchronized to guarantee simultaneous sampling of all selected channels. When this option is not checked, each A/D chip uses its own internal A/D clock to perform conversions, resulting in a conversion time of 2.4us per conversion. (The A/D chip uses four seperate sample-and-hold amplifiers to sample the channels simultaneously and then converts the sampled signals to digital sequentially, with the results stored in an internal FIFO). When this option is checked, the two A/D chips are driven by a common external clock, guaranteeing simultaneous sampling of all channels. However, uses of the external clock results in a slower conversion time of 3.36us per channel.

Output Volts

The output of the Analog Output block is in units of Volts when this option is checked. If this option is not checked, then the output is the raw 14-bit conversion result from the A/D chip. The 14-bit twos-complement conversion result is sign-extended.

Simulation Input

When the Simulation Input box is checked, the block will have an input port. During normal simulation (as opposed to running real-time), the signal at this input will be quantized to the resolution of the A/D and produced at the output. This checkbox has no effect on the real-time code.