Ranges

NI power supplies and SMUs use one or more ranges for voltage and current output, as well as one or more ranges for voltage and current measurement.

Use the highest resolution (smallest) range possible for a particular application to get maximum output and measurement accuracy. Refer to the PXIe-4136 Specifications for more information about what ranges are available for a particular channel on your device.

Note The measurement range is implicitly selected based on the configured output range. Thus, you cannot change the measurement range independently of the output range. The selected measurement range is large enough to measure any voltage or current within the configured output range.

Ranges are typically described as 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 can be configured up to 20 mA.

  • 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

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

Table 12. 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
Pulse voltage level range niDCPower Configure Pulse Voltage Level Range niDCPower_ConfigurePulseVoltageLevelRange
Pulse voltage limit range niDCPower Configure Pulse Voltage Limit Range niDCPower_ConfigurePulseVoltageLimitRange
Pulse current level range niDCPower Configure Pulse Current Level Range niDCPower_ConfigurePulseCurrentLevelRange
Pulse current limit range niDCPower Configure Pulse Current Limit Range niDCPower_ConfigurePulseCurrentLimitRange

When you configure an output range, if you request a range that differs from the ranges described in the PXIe-4136 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.

To change the range, the configured range must be able to accommodate the configured 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 used to measure current. Under loaded conditions, particularly in constant current mode, this will result in glitches at the output. In order to reduce the risk of damage to the DUT, the range change is designed so that the current may be less than programmed but not more.

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

When changing ranges in the Running state, be aware of the order of the output range and output value changes because the configuration change takes effect immediately in this state. To avoid ordering issues, NI recommends that you configure the output range and 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 programmed output (voltage level, voltage limit, current level, and current limit) may be extended beyond their normal operating range on channels that support this feature.

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. Measurements in any given range may be made up to 105% of the range by default without enabling overranging.

Source Autoranging

When source autorange is enabled by setting Source » Output Function, NI-DCPower automatically changes the output range based on the configured output setpoint. NI-DCPower automatically changes to the highest resolution (smallest) range that can accommodate the configured 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 a new setpoint is programmed. Alternatively, you can use Measurement Autorange to have the instrument select the best measurement range. Refer to Measurement Autoranging for more information.

Measurement Autoranging

Use measurement autorange to allow the instrument to select the best measurement range based on the actual measurement values. Set measurement autorange by setting Measurement:Autorange to On.

With measurement autorange, the instrument can change ranges dynamically based on measurement readings; this change in range enables more accurate measurements for both large and small readings. Measurement autoranging removes the need for manual measurement range selection and eases interactive user measurements. For example, this 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, to allow 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.