diff --git a/Python_script/VNA_dummy.py b/Python_script/VNA_dummy.py
index 11a259fdbe97f2258c16ed0b237435a080c2a546..77f8cfd9978ff297fdfff96437bc781d47019ae8 100644
--- a/Python_script/VNA_dummy.py
+++ b/Python_script/VNA_dummy.py
@@ -71,7 +71,7 @@ class VnaDummy:
         return self.simulated_traces
 
     def create_new_trace(self, name, parameter):
-        self.simulated_traces.append((name, parameter))
+        self.simulated_traces.append(name)
 
     def set_trace_measurements(self, trace, measurement):
         pass
@@ -94,8 +94,8 @@ class VnaDummy:
         return '1'
     
     def get_measurement_string(self, trace, result_format):
-
-        self.simulated_traces = trace
+        if trace not in self.simulated_traces:
+            raise Exception('trace '+trace+' is not known to VNA dummy!')
         self.result_format = result_format
 
         phase_radian = self.simulated_phase / 180. * math.pi