Application and Configuration of ADLINK cPCI-9116 Data Acquisition Card

Detailed explanation of ADLINK cPCI-9116 data acquisition card application and configuration

In modern testing and measurement, industrial automation, and scientific research experiments, high-precision and high sampling rate data acquisition cards are the core of the system. ADLINK's cPCI-9116 series 16 bit, 250KS/s analog input card is designed specifically for the 3U CompactPCI platform, integrating rich analog and digital I/O functions, as well as flexible triggering and transmission mechanisms. This article will delve into the application technology key points of cPCI-9116 from the aspects of hardware architecture, signal connection, acquisition mode, trigger configuration, and data transmission, to help engineers quickly get started and maximize its performance.

Overview of Hardware Architecture

CPCI-9116 is a high-performance data acquisition card based on a 32-bit CompactPCI bus, which supports plug and play and does not require manual configuration of base addresses, interrupt numbers, and other resources. The core analog input channel can be configured as follows:

Up to 64 single ended (SE) inputs or 32 differential (DI) inputs;

Single ended and differential can be mixed and flexibly specified through channel gain queues;

16 bit resolution, built-in 1K word A/D FIFO buffer;

The channel gain queue depth is 512 words, and the range and input type of each channel can be independently set (bipolar ± 5V, ± 2.5V, ± 1.25V, ± 0.625V, or unipolar 0-10V, 0-5V, 0-2.5V, 0-1.25V);

The maximum sampling rate is 250KS/s, the analog input accuracy is better than 0.01% FSR (full scale), and the input impedance is as high as 100M Ω | | 6pF.

In addition, the board also provides 8 TTL digital inputs and 8 digital outputs, as well as a 16 bit universal timer/counter that supports internal 24MHz or external clock input.

Analog input signal connection and configuration

The correct signal connection is a prerequisite for obtaining accurate measurement results. The 100 pin SCSI-II connector (J1) of cPCI-9116 provides all analog, digital, and timer signals.

1. Type of signal source

Floating signal source: isolated from the system ground, such as thermocouple, transformer output, optocoupler isolated output. This type of signal requires a bias return path.

Grounding reference signal source: If the signal source is grounded with the system (such as non isolated instrument output), attention should be paid to ground loop interference.

2. Input mode selection

Single ended mode (SE): All signals are referenced to AGND, suitable for floating ground signals, with simple wiring but weak resistance to common mode noise. When multiple floating sources share the same location, the number of connections can be reduced.

Differential mode (DI): Each channel has AIH (high) and AIL (low), and the amplifier responds to the difference between the two, effectively suppressing common mode noise. For the grounding reference source, the differential mode can be directly connected (as shown in Figure 3-3); For floating ground sources, a resistor (approximately 100 times the source impedance) needs to be added between AIL and AGND to provide a bias circuit (as shown in Figure 3-4).

User common mode mode (U_CMMD): When multiple grounded reference sources are grounded together, the signal can be locally grounded to the negative input terminal, and the U_CMMD pin can be grounded to the signal ground. The common mode rejection capability of the instrument amplifier is used to eliminate the ground potential difference (as shown in Figure 3-5).

Engineering Tip: Differential mode has the best noise suppression, but reduces the number of channels by half. The mixed mode allows partial channel SE and partial DI, which need to be specified channel by channel in the channel gain queue.

A/D acquisition working mode

CPCI-9116 supports two basic acquisition modes: software polling mode and programmable scanning acquisition mode.

1. Software polling mode

The simplest way is suitable for single point or low rate requirements. The user initiates a conversion by writing a software trigger bit, and then polls the FIFO empty bit to read data when it is low. Conversion time ≤ 4 μ s, can be read directly with appropriate delay. This mode has an uncontrollable speed and is difficult to achieve a fixed sampling interval.

2. Programmable scanning acquisition mode

To achieve a fixed and accurate sampling rate, this mode must be used. Its core consists of four counters:

SI_comounter (24 bits): The scanning interval determines the time between the start of two scans.

SI_2counter (16 bits): Sampling interval, which refers to the time interval between the conversion of adjacent channels within the scan.

SC_comounter (24 bits): The number of scans collected after triggering (later triggered or middle triggered).

DIV_comounter (9 bits): The number of samples included in each scan, which is the length of the channel gain queue.

Temporal relationship: Sampling interval=SI_2counter/time base; Scan interval=SI_comounter/time base; And it is required that SI_comounter ≥ SI2-Counter × DIV_comounter. The time base can be either an internal 24MHz or an external clock (1-24MHz).