Measurement Specialties USB-1616HS-2 manual Firstportc

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USB-1616HS-2 User's Guide

Functional Details

For example, you set an acquisition to have a scan rate of 100 kHz, which means each scan period is 10 µs. Within the scan period you sample six analog input channels. These are shown in the following figure as channels 1 through 6. The ADC conversion occurs at the beginning of each channel's 1 µs time block.

FIRSTPORTC

Figure 31. Example of FIRSTPORTC or DAC latency

By applying a setpoint on analog input channel 2, that setpoint gets evaluated every 10 µs with respect to the sampled data for channel 2.

Due to the pipelined architecture of the analog-to-digital converter system, the setpoint cannot be evaluated until 2 µs after the ADC conversion. In the example above, the FIRSTPORTC digital output port can be updated no sooner than 2 µs after channel 2 has been sampled, or 3 µs after the start of the scan. This 2 µs delay is due to the pipelined ADC architecture. The setpoint is evaluated 2 µs after the ADC conversion and then FIRSTPORTC can be updated immediately.

The detection circuit works on data that is put into the acquisition stream at the scan rate. This data is acquired according to the pre-acquisition setup (scan group, scan period, etc.) and returned to the PC. Counters are latched into the acquisition stream at the beginning of every scan. The actual counters may be counting much faster than the scan rate, and therefore only every 10th, 100th, or nth count shows up in the acquisition data.

As a result, you can set a small detection window on a totalizing counter channel and have the detection setpoint "stepped over" since the scan period was too long. Even though the counter value stepped into and out of the detection window, the actual values going back to the PC may not. This is true no matter what mode the counter channel is in.

When setting a detection window, keep a scan period in mind. This applies to analog inputs and counter inputs. Quickly changing analog input voltages can step over a setpoint window if not sampled often enough.

There are three possible solutions for overcoming this problem:

Shorten the scan period to give more timing resolution on the counter values or analog values.

Widen the setpoint window by increasing limit A and/or lowering limit B.

A combination of both solutions (1 and 2) could be made.

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Contents Page USB-1616HS-2 Management committed to your satisfaction Trademark and Copyright Information Table of Contents USB-1616HS-2 Users Guide Conventions used in this users guide Where to find more informationAbout this Users Guide What you will learn from this users guideChapter Overview USB-1616HS-2 featuresSoftware features Introducing the USB-1616HS-2Hardware Installing the USB-1616HS-2TR-2U power supply and CA-1* line cord What comes with your USB-1616HS-2 shipment?CA-96A expansion cable Installing the softwareUnpacking the USB-1616HS-2 Additional documentationInstalling the hardware Information on signal connections Configuring the hardwareConnecting the board for I/O operations Connectors, cables main I/O connectorUSB-1616HS-2 screw terminal pin out single-ended connections Screw terminal pin outsDSUB25 expansion connector pin out DSUB25F expansion connectorCA-96A expansion cable CablingUSB-1616HS-2 components Functional DetailsUSB-1616HS-2 components rear view External power connectorUSB-1616HS-2 functional block diagram USB-1616HS-2 block diagramExample Analog channel scanning of voltage inputs Analog inputAnalog input scanning Settling timeAnalog and digital scanning, once per scan mode example Example Analog and digital scanning, once per scan modeAnalog and digital scanning, once per scan mode example Averaging Tips for making accurate temperature measurementsThermocouple input ShieldingAnalog output Digital outputs and pattern generation Digital I/OTriggering Digital input scanningDigital triggering Hardware analog triggeringSoftware-based triggering Stop trigger modes Counter inputsPre-triggering and post-triggering modes Counter modes Totalize modeTips for making high-speed counter measurements 1 MHz Mapped channelsDebounce modes Trigger before stable mode Trigger after stable modeDebounce module Trigger before stable mode Debounce mode comparisonsOptimal debounce time for trigger before stable mode Encoder modeRepresentation of rotary shaft quadrature encoder Maximizing encoder accuracy Connecting the USB-1616HS-2 to an encoderExample Timer outputs Timer outputsTimer output frequency examples Detection setpoint overview Using multiple USB-1616HS-2s per PCCriteria input signal is equal to Action driven by condition Using the setpoint status register Setpoint configurationExamples of control outputs Detecting on analog input, DAC, and Firstportc updatesAnalog inputs with setpoints update on True and False Detection on an analog input, timer output updatesTimer output update on True and False Using the hysteresis functionDetecting setpoints on a totalizing counter Using multiple inputs to control one DAC outputControlling analog, digital, and timer outputs FIRSTPORTC, DAC, or timer update latencyDetection setpoint details Firstportc Calibrating the USB-1616HS-2 Accuracy SpecificationsAnalog input specifications Analog input accuracy specificationsThermocouple TC types and accuracy Note Analog output specificationsAnalog outputs ThermocouplesDigital input/output Digital input/output specificationsInput sequencer Counter specificationsInput sequencer specifications CountersFrequency/pulse generators Power consumptionFrequency/pulse generator specifications Power consumption specifications NoteEnvironmental External powerUSB specifications Signal I/O connectors and pin outUSB-1616HS-2 screw terminal pin out single-ended connections USB-1616HS-2 screw terminal pin out differential connections USA Declaration of ConformityMailinfo@mccdaq.com