--- title: Slow Sweep at Low Frequency description: How to test slow sweeps at low frequencies on a Frequency Response Analyzer. Tips to optimize sweep performance, leveraging high-to-low frequency sweeps image: https://www.venableinstruments.com/hubfs/Auto%20Ranging%20Control%20Stability%20Analysis.jpg --- [![Venable Instruments](https://www.venableinstruments.com/hs-fs/hubfs/VenLogoInst%20%5BConverted%5D-1.png?width=115&height=45&name=VenLogoInst%20%5BConverted%5D-1.png "Venable Instruments")](https://www.venableinstruments.com) Search ## Slow Sweep at Low Frequency *By Ford Mays - January 14, 2025* Recently, a Venable Frequency Response Analyzer user experienced an unusual phenomenon. The FRA was taking a measurement at a very low frequency (100mHz), and took many minutes to complete the measurement. In this blog we will discuss why this happens and what can be done to alleviate the problem. Venable’s FRAs feature auto-ranging measurement channels that simplify operation of the instrument. The user does not have to adjust the input range of the instrument prior to making measurements. However, when starting a sweep at a low frequency, the auto ranging feature can take a long time to settle, as it will have to ‘see’ several cycles of the generator output to optimize the range. The easiest way to alleviate this problem is to start the sweep at the highest frequency to be measured, and sweep down to the lowest. This will allow the auto-ranging inputs to settle in quickly. During the sweep, the measured voltages are not likely to change much, unless there is a resonant point. Another way to resolve this issue is to turn off auto-ranging. This can be done in the Analyzer Control pane of the Venable Stability Analysis Software, under ‘Options’ (see Figure 1.) ![Auto Ranging Control Stability Analysis](https://www.venableinstruments.com/hs-fs/hubfs/Auto%20Ranging%20Control%20Stability%20Analysis.jpg?width=301&height=231&name=Auto%20Ranging%20Control%20Stability%20Analysis.jpg) Figure 1. Auto-ranging Control However, by turning off the auto-ranging feature, one does have to have a pretty good idea what voltages are going to be measured. Since the measured voltages are a function of the generator output, one may have to do some experimenting at various frequencies to determine the appropriate generator output level for a clean plot, and thusly the expected voltages to be measured. Normally, auto-ranging is of great benefit, making the Venable FRA easy to use. However, when starting a sweep at a very low frequency, it can result in very slow sweep times. The easiest way to address this is to sweep from high to low over the frequencies of interest. For additional information on making loop gain measurements, please see these useful blogs: [Did You Know - Adjusting Injection Levels During a Sweep](https://www.venableinstruments.com/blog/adjusting-injection-levels) [How to Use the Servo Function](https://www.venableinstruments.com/blog/servo-loop) [Injection Signal Location and Levels in Loop Gain Measurements](https://www.venableinstruments.com/blog/injection-signal-location-and-levels-in-loop-gain-measurements) [Using the Servo to Set Feedback Loop Injection Levels for Measuring Loop Gain](https://www.venableinstruments.com/blog/using-the-servo-to-set-feedback-loop-injection-levels-for-measuring-loop-gain)   ![iStock-157336072](https://www.venableinstruments.com/hs-fs/hubfs/Web%20Images/iStock-157336072.jpg?width=1000&name=iStock-157336072.jpg "iStock-157336072") #### Distributed Power: What Causes These Systems to Oscillate Distributed power systems can oscillate, especially when driving one power supply with another power supply. Download this white paper to learn what causes distributed power systems to oscillate and how you can prevent oscillation. [![Download White Paper](https://hubspot-no-cache-na2-prod.s3.amazonaws.com/cta/default/4867466/ba09c31a-becf-4e1b-b896-9a0c990c4fc5.png)](https://hubspot-cta-redirect-na2-prod.s3.amazonaws.com/cta/redirect/4867466/ba09c31a-becf-4e1b-b896-9a0c990c4fc5) Comments ### Sign Up for our Blog We promise that we won't SPAM you. #### About Venable Venable provides scalable energy storage and power systems test solutions for precise voltage, current, and frequency measurements, partnering with engineers to ensure battery and power systems around the world will meet stringent field performance demands.  #### Recent news [![Venable Training - Stabilizing Power Supply Control Loops](https://www.venableinstruments.com/hubfs/Venable%20Training%20Front%20Image.jpg) **Venable Training - Stabilizing Power Supply Control Loops** 20 August 2025 ](https://www.venableinstruments.com/blog/stabilizing-power-supply-control-loops) [![The Ins and Outs of System Level Input/Output Impedance Measurements](https://www.venableinstruments.com/hubfs/Imput%20Impedance%20Test%20Set%20UP.jpg) **The Ins and Outs of System Level Input/Output Impedance Measurements** 23 June 2025 ](https://www.venableinstruments.com/blog/impedance-measurements) #### Subscribe Subscribe to our blog to receive emails and updates on scalable power and energy systems test solutions from Venable Instruments.  #### Contact us Venable Instruments 8656 SH 71 West Cuesta Centre, Building E Austin, TX 78735 Office: 512-949-3100 Fax: 512-949-3151