diff --git a/xgm.py b/xgm.py
index d38165e6b2485f86b598aa00e89813f4aee6b94e..40d61ea5443bad06ab7f96eb0db5e2b0a33c09bf 100644
--- a/xgm.py
+++ b/xgm.py
@@ -882,7 +882,8 @@ def autoFindFastAdcPeaks(data, channel=5, threshold=35000, display=False, plot=F
     key = f'FastADC{channel}raw'
     if key not in data:
         raise ValueError(f'{key} not found in data set')
-    trace = data[key].where(data['npulses_sase3']>0, drop=True).isel(trainId=0).values
+    tid = data[key].where(data[key]>threshold, drop=True).trainId[0]
+    trace = data[key].sel(trainId=tid)
     centers, peaks = find_peaks(trace, height=threshold, width=(4, None))
     c = centers[0]
     w = np.average(peaks['widths']).astype(int)