diff --git a/ohmpi/ohmpi.py b/ohmpi/ohmpi.py
index 993bf817627606792ad7d0325edbda0f81053560..9edfc01044220fe609bf5d27d60073ba8d049c57 100644
--- a/ohmpi/ohmpi.py
+++ b/ohmpi/ohmpi.py
@@ -585,9 +585,9 @@ class OhmPi(object):
             self.data_logger.info(dd)
 
             self._hw.switch_mux(electrodes=quad[0:2], roles=['A', 'B'], state='on')
-            self.hw.tx.polarity = 1
+            self._hw.tx.polarity = 1
             time.sleep(1.0)
-            self.hw.tx.polarity = 0
+            self._hw.tx.polarity = 0
             self._hw.switch_mux(electrodes=quad[0:2], roles=['A', 'B'], state='off')
         else:
             self.exec_logger.info(f'Skipping {quad}')