W-14 FAQ MACHINERY MONITORING

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1 FAQ How far can I run an accelerometer cable without loosing signal? Generally, at least a couple of hundred feet. The exact length can be determined knowing the cable capacitance ( picofarads per foot is common) and the available voltage swing (typically at least 5V peak to peak). Given these values, the length of in a function of supply current and highest frequency of interest. Figure 1 shows a chart that helps determine maximium cable lengths. Cables In addition to sensor construction and connector choices, the type of cable and cable material must be carefully chosen to ensure proper operation. The two types of cables most commonly used to connector an accelerometer to acquisition equipment are coaxial and shielded multi-conductor. Coaxial cables carry the power and signal on an inner conductor and have a shield or outer conductor which acts as the signal common. Because coaxial cable works well with BNC and Microdot connectors, it is generally used with either sensors in a walk-around mode or to connect electronic instruments components together. For most sensors, the shielded multi-conductor cable of choice will be a twisted pair, shielded. This type of cable has two conductors, one power/signal and one common, twisted together in order to provide differential cancellation that reduces EMI interference. Surrounding the twisted pair is a foil or braided shield. Proper termination of the shield will protect the conductors from airborne radio frequency interference. Because multi-conductor cable is easy to terminate in the field and offer inherent immunity to environmental noise, it is often the choice for permanent installations. Besides the type of cable, coaxial or multi-conductor, the most important decision for cable selection is material. The intended environment will dictate requirements such as temperature, chemicals, radiation, and moisture. Generally Teflon provides the best temperature and abrasion resistance, although it has a moderate radiation rating. In addition, Teflon generally cannot be used near certain applications, such as tobacco plants. Polyvinylchloride (PVC) provides fair abrasion and chemical resistance, but PVC manufacturers do not recommend its use above 221 F (105 C). Wilcoxon s Enviroprene material is designed to provide excellent performance at a price less than Teflon. With the exception of very hot (>250 F) and abrasive environments, Enviroprene is generally recommended. For long cable runs, the capacitance and resistance of the cable will begin to act as a low-pass filter and cut-off higher frequency data. More supply current will help overcome the resistance and push this filter out higher in frequency. Figure 1: Cable Length vs. Frequency 71

2 Connectors Like sensor selection, choosing a connector to use for the accelerometer is highly dependent on the environment of its intended use. Most industrial accelerometers, piezovelocity sensors and process control vibration transmitters utilize the common 2-pin military connector. Known by its standard designation of MIL-C-5015, this connector style has provided a rugged, simple and cost effective means of connectivity since the inception of industrial vibration monitoring. The MIL-C-5015-style connector is available with a variety of boots and sealing methods for use in different environments. Other connectors, such as BNC, Microdot, bayonet and terminal strips, can be used successfully in appropriate applications. However these connectors lack the Splashproof option of the MIL-C-5015-style connectors and may not adequately resist harsh environment moisture and contaminant penetration into the connector which can short the electrical signal. Terminal strips, BNC connectors and other specialized connectors are often used to connect the sensor cable at the acquisition equipment. An option to having a connector at the accelerometer is an integral cable which attaches directly to the sensor. Underwater sensors, for example, have integral cables which enable deep submersion. Consideration must be given the type of sealing at the cable entry location. TECH TIP Splashproof Connectors Many manufacturers claim to have Splashproof connectors appropriate for harsh environments. In order to qualify the level of sealing, each connector should have an IP (International Protection) rating. Below is a chart describing the IP ratings: LEVEL IP 64 IP65 IP66 IP 67 IP 68 DESCRIPTION Protection against water splash Protection against water jet Protection against powerful water jet Submersible in water 1 meter for minutes Submersible in water > 1 meter continously 72

3 J1 Coaxial, low noise, orange, PVC J3 Coaxial, low noise, high temperature, red, Teflon 100 to to J4 Coaxial, RG 174, black, PVC J5A Coaxial, RG 58, black, PVC 55 to to 221 J6 Coaxial, underwater, black, J8 underwater, black J9 gray, PVC J9A brown, PVC J9B gray, PVC J9T Coaxial, RG 59, black, Teflon 20 J9T2 Tefzel 94 to 2 J9T2A yellow Teflon 73

4 J9T2AS yellow Teflon with stainless J9T2S Tefzel, with stainless 94 to 2 J9T3 white Tefzel 94 to 2 J9T3A yellow Teflon J9T3S white Tefzel, with stainless 94 to 2 J9T4 Four conductor, shielded, red Teflon J9T4A Four conductor, shielded, yellow Teflon J10 gray Enviroprene 50 to to 257 J41 Coaxial, black, PVC, for SNAP sensors J51 Coaxial, retractable, black, PVC J61 Coaxial, underwater, black, 44 J81 underwater, black, WILCOXON RESEARCH, INC TEL FAX sensors@wilcoxon.com WEB 74

5 J81S underwater, black, Polyurethane with stainless J93 Coaxial, RG316/U, high temperature, clear, Teflon 100 to to J95 Five conductor, shielded, black, J96 Teflon J96S Teflon, with stainless *Optional Covers: A = Armor cable covering (available with dia. cables). S = Stainless cable covering (available with most dia. cables). MACHINERY WILCOXON RESEARCH, INC TEL FAX sensors@wilcoxon.com WEB 75