Product Overview
The National Instruments PCI-6221 is a multifunction data acquisition card for PCI based computers. It belongs to the NI M Series DAQ family and provides 16 analog input channels with 16 bit resolution and a maximum single channel sampling rate of 250 kS/s. The card also includes two analog output channels, 24 digital input and output lines, and two counters.
The PCI-6221 installs in a standard PCI slot and is supported by NI-DAQmx software. Its combination of resolution, channel count, and mixed signal functions makes it suitable for automated test, laboratory measurement, and industrial monitoring where a balanced set of capabilities is required.
Analog Input Performance
The card provides 16 analog input channels with 16 bit resolution and a maximum single channel rate of 250 kS/s, with the aggregate rate shared across active channels. Selectable input ranges, including plus or minus 10 V, plus or minus 5 V, and plus or minus 1 V, allow the card to match different signal levels and use the available resolution effectively.
Hardware timed acquisition, external sample clocks, and triggering support repeatable measurement sequences. Multichannel scanning can be configured for single ended or differential connections depending on the accessory and wiring. Differential wiring is often preferred for low level signals and for rejecting common mode noise in industrial environments.
Analog Output and Digital I/O
The card includes two 16 bit analog output channels for control voltages, setpoints, and waveform generation. Hardware timed output produces deterministic waveform sequences, which is useful for stimulus response testing and control loop evaluation. Engineers should verify the load and settling requirements of the driven device.
Twenty four digital lines provide logic level control, relay driving through external conditioning, and status monitoring. Two 32 bit counters support event counting, frequency measurement, pulse generation, and encoder position tracking. Because analog and digital tasks can share timing signals, the card can implement coordinated mixed signal sequences.
Timing and Synchronization
NI-DAQmx provides start triggers, reference triggers, pause triggers, and sample clock configuration for the PCI-6221. These features allow acquisition and generation to be aligned with external events or with other DAQ devices. Counter outputs can be routed as triggers, and analog or digital events can gate tasks.
For larger systems, multiple cards can be synchronized using shared timing and trigger signals where supported. Engineers should document clock sources and trigger routes so that test sequences can be reproduced. Careful planning of channel mapping helps when analyzing data from many sensors.
Software and Accessories
The PCI-6221 is supported by NI-DAQmx and can be programmed with LabVIEW, LabWindows/CVI, Measurement Studio, and other NI-DAQmx compatible environments. The driver handles channel configuration, scaling, calibration metadata, and task management. Screw terminal and mass termination accessories are available for different wiring needs.
Installation requires a PCI slot with adequate airflow and a host computer within the supported specifications. Cables should be routed away from power switching equipment, and shields should be terminated according to the accessory documentation. Regular verification of channel function and calibration supports long term measurement confidence.
Typical Applications
General purpose analog data acquisition
Laboratory measurement and data logging
Automated test with mixed analog and digital signals
Sensor and transducer measurement
Digital control and event counting
PCI based test and measurement systems
The PCI-6221 provides 16 analog inputs at 250 kS/s, 2 analog outputs, 24 digital lines, and 2 counters in an M Series PCI card. Its balanced capabilities and NI-DAQmx support make it suitable for general purpose measurement and control applications.
