Swapped a batch of VAV differential pressure sensors on a 3rd-floor wing and, with the damper overridden to 30% (2–10 V control), BAS flow is reading about 12% low compared to a TSI DP-Calc traverse… Do you correct this at the k-factor in the controller or tune it with input scaling (slope/offset) during calibration to keep sequences and trend data consistent across the network?
@OP I’ve had that after sensor swaps and I correct at the K-factor to keep sequences and trending aligned. Before you touch K, zero the DP with both ports vented, confirm the pickup’s label K is in the controller, and do a second traverse around 70% to see if it’s slope vs. offset.
And @OP Quick tip: don’t set K off a traverse with the “damper overridden to 30%” — drive the box to near design (80–100% open), traverse with the TSI, then adjust K so BAS matches, since low blade angles bias the pickup and you’ll bake in that about 12% error. If it still carries a constant bias across the range afterward, add a small input offset, but leave slope alone to keep sequences consistent.
Building on @vpeterson: I chased a similar 10–15% low after a sensor swap and it turned out the new DP transmitter had square‑root enabled while the controller was also doing it — disable one, set K at near‑design, and recheck. Also make sure your TSI is using the same density (baro/temp) as the BAS; otherwise you’re comparing apples to apple juice.