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Video: What are the different sensitivity settings of a Smart-UPS?

What are the different sensitivity settings of a Smart-UPS?

Product Line:

All models except SURT, SURTA, SURTD, All Serial Numbers

Normal Operation


The Smart-UPS detects line voltage distortions such as spikes, notches, dips, and swells, as well as distortions caused by operation with inexpensive fuel-powered generators. By default, the UPS reacts to distortions by transferring to on-battery operation to protect the equipment that you are plugging into the UPS. Where power quality is poor, the UPS may frequently transfer to on-battery operation. Battery longevity and service life of the UPS may be conserved by reducing the sensitivity of the UPS, as long as your equipment can operate normally under the conditions detailed below. The sensitivity circuit monitors Total Harmonic Distortion(THD), Change in Voltage over Time(dv/dt), and Frequency (Hz) out of tolerance.


The sensitivity circuit looks at these three parameters (THD, dv/dt, Hz) and makes a quantitative analysis based on all three things using a proprietary algorithm.

There are not pre-defined limits for each parameter. (IE: There is no way to say "At medium sensitivity, the UPS will transfer at X percent THD.")

Smart-UPS products default to "High" sensitivity. Lowering the sensitivity may allow your UPS to operate online during a wider array of input conditions, however it also increases the transfer time of the UPS. "Transfer Time" is the length of time a Line-Interactive UPS takes to switch from online to on-battery operation. The level of power disturbance can affect transfer time when the unit is set to Medium or Low. Some sensitive loads may not be compatible with the extended transfer times experienced at lower sensitivity settings. If you experience a load drop during online to on battery transfer when the UPS is set to medium or low sensitivity you may need to increase the sensitivity setting to high. Extremely sensitive loads may perform better with an online UPS such as a Smart-UPS RT which has no transfer time.

High Sensitivity Mode
In the event of any type of voltage disturbance, the UPS will transfer to battery power and watch the AC line until it can transfer back to line. The transfer time in this mode depends on how far the line voltage deviates from the sine wave reference. It is generally 2-4 milliseconds.

Medium Sensitivity Mode
In the event of a RMS voltage-out-of-tolerance(High/Low/No) and RMS-rate-of-change disturbances(dv/dt) in the line voltage, the UPS will transfer to battery power and watch the AC line until it can transfer back to line. In this mode the transfer times are longer but still within acceptable limits to insure the continuity of a computer's operation. They are generally 6-8 milliseconds.

Low Sensitivity Mode
In the event of a RMS voltage-out-of-tolerance disturbances(High/Low/No) in the line voltage, the UPS will transfer to battery power and watch the AC line until it can transfer back to line. In this mode the transfer times are longer but still within acceptable limits to insure the continuity of a computer's operation. They are generally 8-10 milliseconds.

"SU" Smart UPS 700va or larger and "SUA" Smart-UPS 1000va or larger have a sensitivity button on the rear panel of the UPS. To change the sensitivity of the UPS, press the small, white "sensitivity" button* on the rear of the UPS. Use a pointed object (such as a pen) to do so. The default setting is "high"; press the button once to set the sensitivity to "medium", and press it again to set it to "low"; pressing it a third time will set it back to "high". The sensitivity setting change will take effect immediately. The green LED next to the button is a sensitivity setting indicator - brightly lit is "high" sensitivity, dimly lit is "medium", and off is "low" sensitivity.

Next Generation Smart-UPS (Part Numbers beginning with "SMT" or "SMX") feature a fully interactive LCD display. By default these units feature a "Local Power Quality" setting, which is a combination of Sensitivity and Transfer Voltages. To configure sensitivity separately, you must enable "Advanced Menus". This is enabled via the "Configuration" menu on the LCD screen. Once "Advanced Menus" are enabled, you will see several new options under the "Configuration" menu, including "Sensitivity". From there, you can select "Normal" (High), "Reduced" (Medium), or "Low".

  • In any sensitivity mode, a Smart-UPS will transfer to battery when the Frequency(Hz) is out of tolerance(+/-5%).
  • If your model Smart-UPS has neither a sensitivity button or LCD screen, you may still adjust sensitivity via the PowerChute application.
  • Some equipment may be more sensitive to line disturbances. The lower your sensitivity setting, the longer the transfer time. To find out how you equipment may react, please see your equipment manufacturer.

The following video demonstrates how to change the sensitivity settings on the Smart-UPS SMX & SMT models via the display:

APC Austria

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