How do I convert tension specified in pounds for my belt to a Hz reading?
The question of how to convert pounds tension into Hz. is perhaps one of the most often asked questions from people outside of Europe. (In Europe the major manufacturers are now supplying diagrams of belt drives on with the HZ figures attached, so that it is easy!).
Below is a practical approach which does not depend on having any manufacturers data. Manufacturers data will give you both belt length, weight and also often the mass per unit length of the belt.
Stage 1.
The required tension has to converted from lbs to units of Newtons by multiplying by 4.45. As an example for the exercise let us say that the tension is specified at 100lbs. The required tension in newtons is therefore 445.
Stage 2.
The CLAVIS gauge should be used on the longest span of the belt. You need to measure the span length. This is the distance from where the belt leaves one pulley to where it makes contact with the other pulley. You should measure this distance in millimetres. Let us assume for example it is 200mm. which is 0.2 metres.
Stage 3.
You now need to weigh the belt. You should use postal scales or perhaps electronic cooking scales. The weight for a typical automotive timing belt is around 0.1 Kilogrammes (100 grammes) which is only around 3 ozs. So for accuracy it is important that you use sensitive scales. We recommend scales for measuring the weight of letters which can read to 1 gramme. Finally the total length of the belt should be measured. This can be done by laying a flexible tape measure around the outer face of the belt. The belt length for a typical timing belt is around 1200 millimetres or 1.2 metres.
At this point we calculate the mass per unit length of the belt in units of kg/metre, (ie. divide the weight of the belt by the length of the belt)
0.1/1.2 = 0.08 kg/m
Stage 4.
We now have all the information to calculate what the frequency reading should be on the CLAVIS gauge at the correct tension value.
The formula is;
T=4ml2f2
Where;
T is your required tension, in our case 100 lbs, or 445 Newton.
m is the mass per unit length, which we have calculated at 0.08 kg/m
l is the span distance (in metres) which is 0.2 m.
Therefore;
445 = 4 x 0.08 x 0.2 x 0.2 x f2
f2 = 445/4 x 0.08 x 0.2 x 0.2
f2 = 445/0.0128
f2 = 34,765
f= 186Hz
