diff --git a/sensors/SensorDSM501A.h b/sensors/SensorDSM501A.h
index 395f594e..64e1177b 100644
--- a/sensors/SensorDSM501A.h
+++ b/sensors/SensorDSM501A.h
@@ -53,14 +53,16 @@ class SensorDSM501A: public Sensor {
 	
 	// define what to do during loop
 	void onLoop(Child* child) {
-		if (child == children.get(1)) {
-			// get PM 1.0 - density of particles over 1 µm.
-			child->setValue((int)((_getPM(_pin_10)*0.0283168/100/1000) *  (0.08205*_temperature)/0.01));
-		}
-		if (child == children.get(2)) {
-			// get PM 2.5 density of particles over 2.5 µm.
-			child->setValue((int)_getPM(_pin_25));
-		}
+		int ppm = -1;
+		// get PM 1.0 - density of particles over 1 µm.
+		if (child == children.get(1)) ppm = (int)(_getPM(_pin_10));
+		// sleep before the next read
+		nodeManager.sleepOrWait(5000);
+		// get PM 2.5 density of particles over 2.5 µm.
+		if (child == children.get(2)) ppm = (int)(_getPM(_pin_25));
+		// set the value if positive (e.g. negative = invalid read)
+		if (ppm > 0) child->setValue(ppm);
+		else debug(PSTR("!" LOG_SENSOR "READ\n"));
 	};
 	
 	// return PM concentration