Calibrate the NI 6624 using Calibration Executive.

Calibration Executive Procedure Features

Verify Only Verify & Adjust Manual Mode Optional Adjust

Approximate Test Time

Verify only
5 minutes

Test Equipment

The following table lists the test equipment required for calibrating the NI 6624.

Table 83. Test equipment for calibrating the NI 6624
Instrument Recommended Model Requirements
External Counter Agilent HP 53131A or HP 53132A ≤ ppm uncertainty for measurement
+5 Power Source NI 4110 Ability to source current of at least 1 A
Discrete Resistors (x 2) — 5% precision

Resistor Values: 500 Ω
Cable Sh100-100-F —
Connector Block SCB-100 —
CompactPCI-to-PCI adapter — —

Test Conditions

The following setup and environmental conditions are required to ensure the NI 6624 meets published specifications.

  • Keep connections to the device as short as possible. Long cables and wires act as antennas, picking up extra noise that can affect measurements.
  • Verify that all connections to the device, including front panel connections, are secure.
  • Maintain an ambient temperature of 25 °C. The device temperature will be greater than the ambient temperature.
  • Keep relative humidity below 80%.
  • Allow a warm up time of at least 15 minutes to ensure that the measurement circuitry is at a stable operating temperature.
  • Use shielded copper wire for all cable connections to the device. Use twisted-pairs wire to eliminate noise and thermal offsets.
  • Ensure that the PXI chassis fan speed is set to HIGH, that the fan filters are clean, and that the empty slots contain filler panels. For more information, refer to the Maintain Forced-Air Cooling Note to Users document available at ni.com/docs.
  • Plug the chassis and the instrument into the same power strip to avoid ground loops.

Device Setup

To calibrate the onboard crystal oscillator of the PXI-6624, you must calibrate the PXI-6624 on a PCI chassis using a CompactPCI-to-PCI adapter. When using a PXI chassis, the measured frequency is that of the PXI backplane clock instead of the onboard crystal oscillator.

  1. Cable the NI 6624 to a 100-pin connector block.
  2. Wire the +5 V power source to the connector block:
    1. Wire the +5 V power terminal to the connector block terminal that is connected to the PFI 36 Vdd/CTR 0 Vdd pin (pin 7) on the NI 6624.
    2. Wire the ground of the +5 V power source to the connector block terminal that is connected to the PFI 36 Vss/CTR 0 Vss pin (pin 8) on the NI 6624.
  3. Wire a 500 Ω resistor between the connector block terminals that are connected to the PFI 36 Vdd/CTR 0 Vdd pin (pin 7) and PFI 36/CTR 0 OUT pin (pin 9) on the NI 6624. Wire another 500 Ω resistor to the connector block terminal that is connected to the PFI 36/CTR 0 OUT pin (pin 9) on the NI 6624.
  4. Connect the external counter to the connector block using twisted-pair wires:
    1. Wire the input of the external counter to the other end of the 500 Ω resistor that is connected to the PFI 36/CTR 0 OUT pin (pin 9) on the NI 6624.
    2. Wire the ground of the external counter to the connector block terminal that is connected to the PFI 36 Vss/CTR 0 Vss pin (pin 8) on the NI 6624.

Test Limit Equations

The following test limits are derived from the published specifications.

Table 84. NI 6624 Test Limit Equations
Equation Type Equation
Timing Accuracy 1 year limits are calculated as follows:
  • 20MHz Limit = Baseclock Accuracy * Baseclock Frequency = 0.005% * 20M = ±1kHz
  • Baseclock accuracy = ±50ppm (0.005%)