How to correctly read Vibration on IRD811
IRD811 is an Analog Display Vibration Meter. It has two scales for two range multiples.
If you are reading in the multiple of 10, then you need to refer to the top 0 to 1.0 scale and grade it according to your full scale range selection. If you are reading in the multiple of 3, then you need to refer to the bottom 0 to 3 scale and grade it according to your full scale range selection.
Let us see this with an example. Say, your vibration is 10 mm/sec RMS and your full scale knob is set to 10 (
refer Figure 1 Below). To observe this vibration, you will need to look at the 0 to 1.0 scale, where you will have to consider 0 as 0 mm/sec RMS and 1.0 as 10 mm/sec RMS. The needle will deflect from its resting position and stop at the position 1.0 (
refer Figure 2 below) when the vibration is 10 mm/sec RMS in this range selection.
Say, if your vibration was the same i.e 10 mm/sec RMS, but your full scale knob was set to 30 (
refer Figure 3 below). In this event, you would need to read the bottom scale and 0 of the scale would become 0 mm/sec RMS, 1 of the scale would become 10 mm/sec RMS, 2 of the scale would become 20 mm/sec RMS and 3 of the scale would become 30 mm/sec RMS. For your vibration of 10 mm/sec RMS, the needle would deflect from its resting position and stop at the position 1 in the scale of 0 to 3 (
refer Figure 4 below), thereby denoting a vibration of 10 mm/sec RMS.
If you see Figure 4 carefully, then you will see that there are 9 grading lines between positions 1 and 2. Thus, for knob set to 30, these lines would mean a gap of 1 mm/sec RMS. If your vibration was 15.6 mm/sec RMS, then the needle would stop between positions 15 and 16 on the 0 to 30 scale. You would need to report it as 15-16 mm/sec RMS as the meter will not be able to tell you whether it is exact 15.6 mm/sec RMS