Informationen zu:

• FFT
• Oversampling
• Trigger
• PWM
• Digital Filter

Local intelligence

The USB bus fragments packets and sends them at a rate of 1000 Hz, i.e. 1 packet per ms. With USB 2, these packets are divided into 8 microframes. All data sent to or from the USB device must be packaged by this packet. Thus the controllability of the computer via the USB bus is very much slowed down, since it can send a command a maximum of once per millisecond. For bidirectional communication, the command must first be sent, the response received, the controller calculated and then sent again until an event-dependent controller sets a new value. This is very slow for time-critical control. The signal processor, which the Multichoice USB cards all use, shifts the intelligence to the measurement card. Regulation and control can take place directly on the measurement card, so that the PC and the slow communication via the packets are decoupled from the actual regulation. The PC then only transmits changed default parameters to the measurement card.

Local storage

Due to the delays caused by the USB bus, the measured values ​​have to be buffered on the cards in order to guarantee uninterrupted data transfer and the consistency of the measured data. Ideally, an endlessly large buffer is available for each type of measurement. Since this is not technically feasible, the existing 1.5 MByte memory is used flexibly with the measurement cards of the Multichoice USB series and distributed to the existing measurement types, so that the maximum possible for these functions is always available.

Signal processor for maximum flexibility

The Multichoice USB cards have a signal processor that can take on a variety of other tasks in addition to the pure acquisition and output of measured values. Signals can be generated and calculated in real time, filters, PID controls, FFT and a large number of other functions can be calculated and carried out at runtime, the accuracy of the measurement can be increased even more through multiple sampling and arithmetic averaging (oversampling), and much more.

Multi-function counter

All Multichoice PCI and USB data acquisition cards have the most modern counters implemented in an FPGA. These own counters not only support the pulse counting and fixed frequency measurement modes, as is the case with standard counter modules, but each counter channel offers a selection of pulse counting (forwards / backwards), frequency measurement with 4 adjustable resolutions, period measurement and pulse width measurement. In addition, incremental counters and SSI interfaces are available to complete the range of counters. Pulse width output with simultaneous frequency modulation round off the output options.

Flexible configuration

The signal inputs of the Multichoice USB are maximally configurable. In addition to the amplification of 1x, 2x, 4x and 8x, each channel can be switched between the bipolar and unipolar measuring range in order to guarantee the optimal resolution for the expected measuring range. The direction of the digital inputs / outputs can be switched and used as inputs or outputs, so that the number of inputs and outputs can be freely defined depending on the application.

High performance

The data on the measurement cards for the maximum read-in and output rates are those actually achieved with the specified accuracy. In many cases, information on the performance can be found from other providers, which on closer inspection and high sampling rates tend to inaccuracies.

Pulse width output without interruptions

The pulse width outputs of the multichoice cards are tear-free. In contrast to many PWMs available on the market, when new specifications are written, the previous period is only ended before the new value is adopted. This guarantees that no phase jumps occur, which is essential when controlling proportional valves.

High protection of the measuring card

The analog inputs of the Multichoice USB are voltage-proof up to + – 40V when switched on and off, so that even higher voltage peaks do not damage the multiplexer

High number of channels

The measurement cards are available with up to 32 analog inputs, plus 2 counters, 4 analog outputs and 24 digital inputs / outputs. Pulse width modulation, incremental counter and SSI interface can also be added as an option. If more channels are required, up to 4 measurement cards can be operated in parallel.