AGE SCIENTIFIC - Products - WaLrus/WWalrus

Strain and vibration can be commonly measured using strain-gauge sensors. The strain-gauge is a strain dependent resistor whose value has very little displacements from the nominal value. The displacement can be some percentage of the nominal value, few Ohm from a typical value of 120 Ohm. Due to the electronic noise the resistor value measurement is very difficult. Usually the strain-gauge is installed in one or two Wheatstone bridge branches. The bridge unbalance is amplified by a differential amplifier. The sensor is glued on the part under test, often in a difficult access situation. Whenever this happens the strain-gauge is connected to the front-end electronics by cables long enough resulting in one or more of the following troubles:
· the connection cables ohmic resistance can cause a voltage drop. This results in a wrong bridge drive and consequently in a wrong measurement because the sensitivity depends from such bridge voltage drive. When possible the problem can be avoided reducing the connection length or using a Kelvin probe;
· the connection cables can be microfonic enough to worsen the measurement. Also in this case cutting the cables length reduce the problem.
· the strain-gauges are low value resistors so the relevant measurement is very sensitive to the surrounding electro-magnetic fields. Every electro-magnetic source as an electric motor or a power inverter must be kept as far away as possible. Often the measurement cannot be performed far away from some of these noisy sources.

Many times the troubles explained above are avoidable performing a good choice in the cable quality and in the way the sensor is cabled. In other situations the sensor cabling is impossible, for example measuring the strain and the vibration of a rotating shaft. The WaLruS and the WWaLruS are electronic equipments for solving all the cabling troubles in the strain-gauge data acquisition. The WaLruS and the WWaLruS are very compact electronic equipments so they can be installed very close to the sensor bridges. Using the WaLruS and the WWaLruS the physical connection between the sensor and the front-end electronics can be reduced to millimetric length. Moreover the WaLruS and the WWaLruS outputs are just digital data, ready for a direct acquisition via a common Personal Computer serial port. The resolution of the output data is 10 bits, the output data rate is 1 kHz data rate for the WaLruS and 2 kHz for the WWaLruS. The WaLruS is connected to the PC via a radio-link, overcoming every situation of impossible cable connection. The rotating shaft is one example. The WWaLruS is even smaller than the WaLruS and it's connected to the PC via a four wires cable.. The WWaLruS output data travel through the cable just in digital format. This results in excellent noise immunity. So the WWaLruS is the best choice whenever the measurement must be performed in very noisy environmental conditions or very far away from the PC. Because of its small dimensions the WWaLruS is suitable in every narrow space situation. Both WaLruS and WWaLruS perform an high performance a high quality digital acquisition of strain gauge at very low price.