Transducer snubbing need no longer be guesswork. Using our new Lohm law for snubbers it is easy to select the correct Visco snubber for every application. Typical applications involve snubbing a cyclic pressure ripple superimposed on a steady pressure. The graph below together with the formula below provide a rapid means of calculating the necessary Lohm rate.
TO FIND A LOHM RATE
Decide how much attenuation is required and use the graph below to obtain a value for fo . Use this in the formula below and solve for Lohm rate.
L = Fluid resistance (Lohms)
fo = Frequency from graph (Hz)
fr = Ripple frequency (Hz)
v* = Internal volume of the transducer (in3)
B = Fluid bulk modulus (psi)
K* = Transducer compliance (in3/psi)
Po = Ripple amplitude, peak-to-peak (psi)
*Obtainable from the transducer manufacturer.
A pressure transducer is being damaged by a pump ripple of 270 Hz. The peak-to-peak amplitude is 1000 psi. Knowing the transducer has an internal volume of 0.09 in3 (1.5 mL) and a compliance of 3 x 10-7 in3/psi, which Visco snubber is required to reduce the ripple to 1/20 of the unsnubbed amplitude? The fluid is Skydrol with a bulk modulus of 340,000 psi.
Obtain f0 from the graph (170 Hz at 0.05 amplitude ratio.) Then use the formula:
Use Visco snubber Part Number VHSA1250800H (80,000 Lohms).