2. Electrical Basics for sensors (Dynamic vs. PC420 series) What is Ohm’s law ? How does a “constant current/voltage modulated” sensor work ? How does a “Loop Powered Sensor” work ? What’s the difference ?
3. Ohm’s Law Mathematical expressions of Ohm’s law: V=I*R I=V/R R=V/I where: V is Voltage, I is Current, and R is Resistance Each of these equations is identical, they are simply re-arranged to solve for one particular variable.
4. Ohm’s Law - Units and Symbols Voltage: Expressed in Volts or V, and possibly modified by (Alternating Current) as VAC or (Direct Current) as VDC Current: Expressed in Amperes, Amps or A Resistance: Expressed in Ohms or Unit multipliers: k = kilo = 1,000 ; M = Mega = 1,000,000 m = milli = 1/1,000 ; p = pico = 1/1,000,000 Examples: 100 millivolts = 0.1 volts ; 20 milliamps = 0.02 amps 1.5 kVDC = 1,500 Volts DC
5. Ohm’s Law - Circuit example V = I * R I = V / R R = V / I Example 1: R = 250 , I = 20 mA ; find V V = 0.020 x 250 = 5.0 volts Example 2: V = 1.0 volt, R = 250 ; find I I = 1.0 / 250 = 0.004
11. 4-20 mA Loop Powered Sensor (LPS™) The sensor controls the current flowing in the loop 0.0 inch/sec. = 4 ma 1.0 inch/sec. = 20 ma Example: Voltage Output @ 1 in/sec = .02 x 250 = 5 volts ; @ 0 in/sec = .004 x 250 = 1.0 volt V+ = 24 VDC, R = 250
12. What’s the difference ? Piezo FET ® style VOLTAGE output AC output DYNAMIC sensors LPS™ Sensors CURRENT output DC output STATIC sensor output
15. Time Response of LPS™ The PC420 output follows the signal peak The PC420 has a 1 to 2 second ‘lag’ in responding to a sudden shift
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17. Why would anyone want an LPS™ ? Connecting an LPS™ to a plant’s Distributed Control System (DCS) or a Programmable Logic Controller (PLC), allows the overall vibration of machinery to be monitored more frequently than a plant’s predictive vibration program. Trending this overall vibration can spot trouble faster than a plant’s predictive vibration program. This is very valuable for critical machinery. The data can be made available to machine operators .
18. Who usually buys this kind of sensor ? Initially, the predictive vibration group would have to be involved in the selection of a PC420 sensor. Usually the sensors are purchased by the Instrument & Electronic ( I&E ) group. The money usually comes from the production budget, not the maintenance budget. There is always more money available from the production budget than from the maintenance budget.