Validating your furnace is a complex process requiring temperature uniformity surveys (TUS) and system accuracy tests (SAT). You also have to properly tune your furnace by adjusting your PID and DigiTrim® controls settings. In an earlier post, we examined some of the basic steps and considerations for PID tuning; however, it is important to adjust your DigiTrim controls settings to achieve the tightest tolerance possible before final PID adjustments are made.
DigiTrim controls are a factory preset on the majority of Ipsen vacuum furnaces, and they allow you to fine-tune the power output to individual heating zones and ensure all heating zones are within the required ± tolerance. DigiTrim controls are one of the settings you adjust to help balance the load and ensure the overall temperature uniformity is within the desired range (e.g., most furnaces require that the temperature uniformity be within ±10 °F from the desired set point).
Ipsen’s standard is to have three primary areas of tuning, also known as trim zones, associated with DigiTrim controls: the front, middle and rear zones. The power output percentages for each of these three trim zones can be adjusted as necessary to obtain a tighter temperature uniformity throughout the work zone. Depending on the hot zone design you have, certain zones may be set upwards to 100 percent to make up for heat loss and ensure a uniform temperature throughout the furnace. The ability to tune each individual trim zone also provides the furnace user with the flexibility to make precise adjustments and ensure improved accuracy for the TUS reports.
Since you are able to see the precise number each zone is set at – rather than attempting to tune a rheostat dial – you can document the exact settings, which allows for increased repeatability and lets you see if any undocumented adjustments have been made since you last performed a TUS.
When tuning your DigiTrim controls settings, it is also important to note that there are five sets of adjustable temperature ranges for tuning the furnace’s temperatures and ramp settings, as well as avoiding possible overshooting. Since all of this is digital, you can provide different settings that tune at various temperature ranges, allowing you to run a variety of load configurations – all at the desired temperatures.
However, it is important to know which temperature ranges you will be tuning at prior to beginning any surveys, as well as the desired tolerance range for your specific equipment. This is because certain specifications have set allowable temperature ranges. For example, AMS 2750 mandates that you adhere to certain temperature ranges and deviations specific to the classification to which you are testing.
Best Practices
When tuning your DigiTrim controls settings, some best practices should be kept in mind to simplify the process. However, it is important to recognize that tuning your controls is still a time commitment. Here are three recommended steps for making the tuning process as smooth and quick as possible:
- Before making any adjustments, document and record all previous adjustments, then allow the furnace adequate time to stabilize at each temperature set point prior to tuning.
- Only make one adjustment at a time; this helps avoid having to start over because too large of an adjustment was made, or because you don’t know the true cause and effect of each incremental step when combined.
- After each adjustment, allow the furnace to stabilize for at least 15 minutes to reach a steady-state heat loss; this also allows you to determine if the adjustment made produced the desired effect.
If you need further assistance with tuning your DigiTrim controls settings, please contact Ipsen at 1-844-GO-IPSEN.