diff --git a/hardware/ohmpi_card_3_15.py b/hardware/ohmpi_card_3_15.py
index 2d82b8accc803e4e844f5fce7f4c8206f0c4d94f..cd6f45506eca3907a00d8c35d5ea040bc4dad2c6 100644
--- a/hardware/ohmpi_card_3_15.py
+++ b/hardware/ohmpi_card_3_15.py
@@ -193,7 +193,7 @@ class Tx(TxAbstract):
         if polarity is None:
             polarity = self.polarity
         self.polarity = polarity
-        self.voltage(voltage)
+        self.voltage = voltage
         self.exec_logger.debug(f'Voltage pulse of {polarity*voltage:.3f} V for {length:.3f} s')
         self.inject(state='on')
         time.sleep(length)