Noise caused by Inductive Coupling

Noise caused by Inductive Coupling
Electrical cable အတြင္း current ျဖတ္သန္းစီးဆင္းသြားေသာအခါ ၎ပတ္လည္တြင္ magnetic field ျဖစ္ေပၚလာသည္။ Electrical current သယ္ေဆာင္လာေသာ wire ႏွစ္ေခ်ာင္းကို အၿပိဳင္သြယ္တန္းထားသြားေသာအခါ magnetic field အခ်င္းခ်င္းသက္ေရာက္မႈေၾကာင့္ cable တေလ်ာက္ noise voltage ကို ျဖစ္ေပၚေစသည္။ Power cable ႏွင့္ Instrument signal cable ကို အၿပိဳင္သြယ္တန္းထားေသာအခါ ပိုမိုသိသာထင္ရွားလာျပီး instrument signal cable အတြင္းျဖစ္ေပၚလာေသာ noise voltage သည္ analog signal မ်ားကိုပ်က္စီးေစသည္။
Power Cable ႏွင့္ Instrument Signal Cable အတြက္သီးျခား conduit (သို႔) duck ျဖင့္သံုးျခင္း၊Instrument မ်ားအတြက္ cable ကို twisted pair သံုးျခင္းျဖင့္ inductive coupling ေၾကာင့္ျဖစ္ေပၚလာေသာ noise ကို တားဆီးႏိုင္သည္။

Noise caused by Capacity Coupling

Noise caused by Capacity Coupling
Electrical Cable အတြင္း current စီးဆင္းသြားေသာအခါ electrical cable conductor မ်ားအၾကားရိွေနေသာေလထုသည္ dielectric (insultaing substance) သဖြယ္ျဖစ္ေပၚလာသည္။ Capacitor သေဘာအရ conductor ႏွစ္ခုအၾကားရိွ insulating substance ကိုျဖတ္သန္း၍ conducative path ျဖစ္ေပၚလာကာ AC signal စီးဆင္းျခင္းေၾကာင့္ noise voltage ကိုျဖစ္ေပၚေစသည္။
၁။Power Cable ႏွင့္ Instrument Signal Cable အတြက္သီးျခား conduit (သို႔) duck ျဖင့္သံုးျခင္း၊
၂။Instrument မ်ားအတြက္ cable ကို twisted pair သံုးျခင္း၊
၃။Instrument မ်ားအတြက္ Shield wire သံုးျခင္း၊
ျဖင့္ capacity coupling ေၾကာင့္ျဖစ္ေပၚလာေသာ noise ကို တားဆီးႏိုင္သည္

Understanding PID in 4 minutes

Understanding PID in 4 minutes

Pressure Gauge

Industrial Valve Symbol

Valve Symbol

Thermistor                                         

The Thermally sensitive resistors(Thermistors) are similar to electrical resistors whose resistance changes with temperature. Thermistors are made of semiconductor material. There are 2 types of thermistors:

1. PTC (positive thermal coefficient) which increases it's resistance with increasing temperature.
2. NTC(negative thermal coefficient) which decreases it's resistance with increasing temperature. The NTC is the most common among the two types of thermistors.

Advantages of thermistors
• more sensitive than the RTD's and thermocouples
• Small sizes
• Quick response
• Low cost
• Suitability for narrow spans

Disadvantages of thermistors
• Linearity is not good
• More susceptible to permanent decalibration at high temperatures
• Use is limited to a few hundred degrees Celsius
• Respond quickly to temperature changes, especially susceptible to self-heating errors
• Very fragile

Applications of thermistors
Due to it's low cost and high sensitivity,it is widely used in the applications such as the winding temperature of motors, or the temperature of bearings, or the temperature of transformer windings in which the actual temperature may not be of as much concern as the change or rapid increase in temperature . Many consumer-grade devices use thermistors for temperature sensors too.
A PTC is used as a current limiter. As the current increases the temperature increases. hence the resistance increases limiting the current.