NI power supplies and SMUs use one or more ranges for the following:

  • Voltage and current output
  • Voltage and current measurement

To get maximum output and measurement accuracy, use the highest resolution (smallest) range possible for a particular application. Refer to the PXIe-4147 Specifications for more information about what ranges are available for a particular channel on your device.

Note NI-DCPower implicitly selects the measurement range that is based on the output range that you configure. Thus, you cannot change the measurement range independently of the output range. The measurement range is large enough to measure any voltage or current within the output range that you configure.

Ranges are the maximum possible value from zero that the range can output or measure (not including the overrange). For example, in the 20 mA current level range, the current level is configurable up to 20 mA.

Note
  • When niDCPower Configure Output Function is set to DC Voltage, the voltage level range and current limit range are in use.
  • When niDCPower Configure Output Function is set to DC Current, the current level range and voltage limit range are in use.

The same relationships hold true during pulsing between pulse output functions, pulse level ranges, and pulse limit ranges.

Changing Ranges

When you configure an output range, if you request a range that differs from the ranges described in the PXIe-4147 Specifications, NI-DCPower selects the highest resolution (smallest) range available that accommodates the requested range. For example, on a device with only 20 mA and 200 mA current limit ranges, if you request 100 mA for the current range, NI-DCPower selects the 200 mA range.

The following table lists the supported configurable output ranges and their VIs and functions.

Table 14. Supported Configurable Output Ranges for Each Device Channel
Range VI Function
Voltage level range niDCPower Configure Voltage Level Range niDCPower_ConfigureVoltageLevelRange
Voltage limit range niDCPower Configure Voltage Limit Range niDCPower_ConfigureVoltageLimitRange
Current level range niDCPower Configure Current Level Range niDCPower_ConfigureCurrentLevelRange
Current limit range niDCPower Configure Current Limit Range niDCPower_ConfigureCurrentLimitRange

To change the range, ensure that the range you configure can accommodate the output value. For example, if the current limit range is 1 A and the current limit is 50 mA, changing the current limit range to 20 mA is not allowed because 50 mA is not possible in the new range.

Note Changing current ranges implies a change in the shunts that measure current. Under loaded conditions, particularly in constant current mode, this results in glitches at the output. To reduce the risk of damage to the DUT, the range change is designed so that the current might be less than what you program but not more.

Level and limit changes occur simultaneously when a range change is not required. The changes occur when you apply the channel configuration upon entering the Running state. However, changes do not occur simultaneously if a voltage or a current range change is involved.

Tip When you change ranges in the Running state, the configuration takes effect immediately. Ensure that you are aware of the order of the output range and the output value changes. To avoid ordering issues, NI recommends configuring the output range and the output value in the Uncommitted state and then transition to the Running state. Alternatively, you can enable autoranging for the range you want to change.

Overranging

If niDCPower Overranging Enabled is set to TRUE, the valid values for the output that you program (voltage level, voltage limit, current level, and current limit) may extend beyond their normal operating range on channels that support overranging.

Enabling overranging for a particular channel extends voltage and current output capabilities from 100% to 105% for the output range. Overranging is applicable to output ranges only and does not apply to measurement ranges. You can perform measurements in any given range up to 105% of the range by default without enabling overranging.

Source Autorange

When you enable source autorange by setting Source:OutputFunction, NI-DCPower automatically changes the output range based on the output setpoint that you configure. NI-DCPower automatically changes to the highest resolution (smallest) range that can accommodate the output value. You can selectively enable source voltage level/limit and current limit/level autorange on a channel.

Note While source autorange selects the best range based on the setpoint, it does not change the range until you program a new setpoint. Alternatively, you can use measurement autorange to allow the instrument to select the best measurement range. Refer to Measurement Autorange for more information.

Measurement Autorange

Use the measurement autorange to allow the device to select the best measurement range based on the actual measurement values.

To enable measurement autorange, set Measurement:Autorange to On.

With measurement autorange, the device can change ranges dynamically based on measurement readings, enabling more accurate measurements for both large and small readings. Measurement autorange removes the need for manual measurement range selection and eases interactive user measurements. For example, measurement autorange is useful when the DUT varies significantly in current for a given voltage sweep.

Measurement readings are Current when sourcing voltage and Voltage when sourcing current.

A range change occurs after the hardware evaluates an autorange aperture sample against the configured thresholds. The autorange aperture is configurable, but is generally less than or equal to the measurement aperture setting when Autorange Aperture Time Mode is set to Auto.

The firmware automatically delays the measure trigger after a range change to improve consistency and reduce sweep test times. The delay after range change automatically increases with source delay, allowing for a longer DUT settling time before measuring. You can program the maximum delay after range change.

You can configure measurement autorange for a variety of DUTs through settings for multiple thresholds, limited autorange, and autorange.