diff --git a/Source/DeviceThread.cpp b/Source/DeviceThread.cpp
index 6ee2e2c..cf4ec03 100644
--- a/Source/DeviceThread.cpp
+++ b/Source/DeviceThread.cpp
@@ -2136,10 +2136,13 @@ short DeviceThread::getAdcRange(int channel) const
 void DeviceThread::runImpedanceTest()
 {
     if (!checkBoardMem()) return;
-    impedanceThread->stopThreadSafely();
+
+    setSampleRate(Rhd2000ONIBoard::SampleRate30000Hz, true, false); // set to 30 kHz temporarily
 
     impedanceThread->runThread();
 
+    setSampleRate(settings.savedSampleRateIndex, false, true); // set to 30 kHz temporarily
+
 }
 
 
diff --git a/Source/ImpedanceMeter.cpp b/Source/ImpedanceMeter.cpp
index 39b0596..2ddcb19 100644
--- a/Source/ImpedanceMeter.cpp
+++ b/Source/ImpedanceMeter.cpp
@@ -359,8 +359,10 @@ void ImpedanceMeter::runImpedanceMeasurement(Impedances& impedances)
     int numPeriods = (0.020 * actualImpedanceFreq); // Test each channel for at least 20 msec...
     if (numPeriods < 5) numPeriods = 5; // ...but always measure across no fewer than 5 complete periods
     double period = board->settings.boardSampleRate / actualImpedanceFreq;
-    int numBlocks = ceil((numPeriods + 2.0) * period / 60.0);  // + 2 periods to give time to settle initially
+    int numBlocks = ceil((numPeriods + 2) * period / float(SAMPLES_PER_DATA_BLOCK(board->evalBoard->isUSB3())));  // + 2 periods to give time to settle initially
+    LOGD("ImpedanceMeter: Initial numBlocks = ", numBlocks);
     if (numBlocks < 2) numBlocks = 2;   // need first block for command to switch channels to take effect.
+    LOGD("ImpedanceMeter: Padded numBlocks = ", numBlocks);
 
     CHECK_EXIT;
     board->settings.dsp.cutoffFreq = board->chipRegisters.setDspCutoffFreq(board->settings.dsp.cutoffFreq);