The PXIe-4133 supports two methods of contact checking: the Low Voltage Contact Check function and the Contact Check function. The Low Voltage Contact Check more strictly limits the available output voltage and current. This may be important when probing potentially sensitive circuits or structures. The Contact Check function supports higher voltages and currents, which may be desirable when trying to forward bias a diode junction during the contact check.

Summary of the contact check methods:

Low Voltage Contact Check

  • Outputs voltage up to 0.5 V between Force_HI and Force_LO
  • Short circuit limited to 650 μA
  • Measures current (0 to 100 μA range) out of Force_HI pin
  • Measures voltage between Sense_HI and Sense_LO pins (remote sense, 4-wire mode)

Contact Check

  • Outputs current up to 10 mA from Force_HI to Force_LO
  • Voltage clamp programmable up to 5 V between Force_HI and Force_LO
  • Measures current into Force_LO pin
  • Measures voltage across Force pins (local sense, 2-wire mode) or Sense pins (remote sense, 4-wire mode)

With the Contact Check function, the PXIe-4133 pulses a test current in the same manner as the normal Pulse Current mode, but with the addition of an output voltage clamp. Current is driven out of the Force_HI pin and returns through and is measured at the Force_LO pin. You can read back the voltage either from the local sense (Force_HI and Force_LO, 2-wire mode) or from remote sense (Sense_HI and Sense_LO, 4-wire mode). The voltage clamp is placed between the Force_HI and Force_LO (across the current source) so selecting between local and remote sense has no impact on the current or the output voltage.

In the Contact Check mode, the current source has a 1 kOhm output impedance, and the voltage clamp has a 50 Ohm impedance. The following figure shows the resulting Current vs Voltage profile with the output current set to 10 mA and voltage clamps set for 1 V to 5 V.

The low voltage contact check function limits the possible voltage and current to much lower energy levels for validating contact with more sensitive circuits and structures. The Low Voltage contact check applies a small configurable bias voltage (up to 500 mV) between Force_HI and Force_LO. The current that flows out of the Force_HI pin is measured within a range of 0 to 100 μA, and is limited to about 650 μA in case of short circuits.

Low Voltage Contact Check also reads the voltage between Sense_HI and Sense_LO. Sense_HI and Sense_LO are only used to read voltage; the voltage on the Sense lines does not impact the Force current and voltage. Low Voltage Contact Check does not support Local Sense mode; the voltage between the Force pings is not read back directly.

In the Low Voltage Contact Check mode, the configurable output voltage has an impedance of about 120 Ohms. There is a 640 μA current limiter with an impedance of 5 kOhm. The following figure shows the resulting Current vs Voltage profile with the output voltage at settings between 50 mV and 500 mV.

Use the LowVoltageContactCheck() function to perform a Low Voltage Contact Check. Although the short-circuit current limit is set to 600 μA, the current measurement range is only 0 μA to 100 μA. An open circuit reads near zero μA. To tell that contact is made and current is flowing, the device you are contacting must be conducting at least several microamps at the test voltage you select (up to 500 mV).