Usage Notice of Potentiometer

¡@¡@In order to use the potentiometer under the steadiest conditions,please pay attention to the influence of the following factors on the potentiometer:

Influence of the environment:

1 ¡B Ambient temperature

¡@¡@When the ambient temperature is over 70 ¢J ,the rated power of the potentiometer will drop remarkably.

¡@¡@The turning/sliding operating torque/force lessens with the rise of temperature and increases with the drop of it.If the potentiometer is to be used under low temperature,please contact us .We have special grease to normalize the turning torque under low temperature.

2 ¡B Chemicals

¡@¡@Since synthetic resins such as polycarbonate have been used in potentiometer,please keep the potentiometer away from the following substances:ammonia,alkaline solution,aromatic hydrocarbon,haloid hydrocarbon,ketone,lipid and other strong chemicals.

•  Corrosive gas

¡@¡@Avoid using the potentiometer in harmful gases such as SO 2 NH 3 ,which will lead to corrosion of plastics or metal.

•  Dew formation

¡@¡@Dew formation or water drops on the surface of potentiometers should be avoided.Don't use the potentiometer in humid places or where moiseture can easily condense on element surface,otherwise,insulation deterioration or short-circuiting will take place.

Influence of soldering conditions and method

•  During soldering ,the potentiometer may be damaged due to over temperature or long soldering time.The recommended soldering conditions are:temperature of 235 ¢J ¡Ó5 ¢J soldering time within 3 seconds,and the soldering point should be at least 1.5mm from the main body of the potentiometer.If soldering iron is used,please choose electric soldering iron of lower power and finish soldering in 2 seconds.

•  Do the soldering from the back of the PC board ,I.e.the back of the mounting sice of the potentiometer; no solder should be allowed to flow through the circuit board in order to prevent the heat from transferring too quick and damaging the potentiometer(see figure 1).

•  Please pay attention that no soldering flux is allowed to infiltrate into the potentiometer,otherwise,there will be poor contact between brush and the resistor ,and leading to INT damaging,noise,etc. Therefore ,if ware soldering is employed is employed ,please adopt proper precautions.

•  Water-soluble soldering flux should be avoided.Otherwise,metal oxidation and mould development on materials will be aggravated.

•  Avoid using solder of poor quality,which may lead to difficulty in applying the solder,and resulting in poor contact or open circuit.

Influence of mounting method:

•  When the potentiometer is fixed onto the board by nut ,be careful when tightening the nut.The tightening torque should not be too high to prevent damaging the screw thread.

•  When screw is needed for mounting shell type sliding potentiometer,avoid screws of excessive length,otherwise the movement of the sliding bar may be hindered even the potentiometer be damaged.

•  Don't exert too much force on terminals during soldering or mounting ,otherwise,poor contact even mechanical damage may be found.Avoid bending terminals back and forth because the terminal may break due to two circles of bending or more.

•  When assemble the knob,don't exert over axial pushing/pulling force on the shaft.The force must not exceed the shaft pushing /pulling force set in the Specification Table.

Storage conditions

•  High temperature,high humidity or corrosive gases are prohibited in storage.

•  Don't open the seal when long-term reservation is needed.

•  Keep the principle of ¡§first come,first use¡¨.

Suggestions on circuit design and layout:

•  Because of the existence of resistance value,the potentiometer will produce heat quantity under applied load.

Please take this into account during design.

•  The best way is to use the potentiometer as a four-terminal element for adjusting voltage of voltage divider.For wiring,you'd better choose terminal ¡§1¡¨ for grounding and RL(the load resistance of the potentiometer)should be not smaller than ten times as RT(the nominal resistance).

¡@¡@Except for special design requirement,the potentiometer shouldn't be used as a two-terminal rheostat.The contact resistance between the resistor and the contact piece will hinder the passing of big electric current ,at the same time,the current at the moving contact may be too big since only part of the effective travel is in function and lead to local over loading then failure of the unit,(See figure 2B)

•  When the potentiometer is used as current regulator in DC circuit ,DC current will pass the sliding arm thus resistance value will rise abnormally because of anodic oxidation .In this case,it is recommended to connect the leading-out terminal of the resistor to the cathode and that of the sliding arm to anode .(See figure 3)

•  Although both poles of the resistor are covered by printed silver layer,normally a carbon film is applied on the pole in order to improve reliability of sulfide resistance,and causing a comparatively high terminal resistance. If lower terminal resistance is needed,please contact us.

•  Too much twisting force on the limit stop of the turning knob may give rise to mechanical damage. Therefore,please choose knob of smaller outside diameter to minimize torque on the stop.

•  For shaft type potentiometer,please make proper design to enable the user to turn the knob on shaft handle by hold the knob with thumb and forefinger from two different directions.The reason is that when force on the shaft handle is evenly applied ,the shaft will be more steady and contact between the brush and the resistor will be more reliable.(See figure 4)

•  Sufficient fitting clearance should be arranged when calculating the diameter of the mounting hole prepared for the adjusting knob in the panel .Too tight fitting together with deviation of knob centerline and unsteadiness of the shaft handle will cause scraping and friction between the knob and the panel.(See figure 5)

•  When select the sliding handle for sliding type potentiometer or shaft handle for the turning type,choose as short as possible.When the handle becomes shorter,the handling and the movement become steadier.(See figure 6)

•  For driving unit of the sliding handle in sliding type potentiometers,it is not proper to allow displacement between the contact spot and the centerline of the handle. The smaller distance L is ,the better the sliding control by hand will be. You'd better use a driving unit in which the driving piece and the handle has the same centerline.(See figure 7)

•  or potentiometers with switches,please use it within the rated power of the switch .Don't use a high power switch as small current circulation and on-and-off switch.For example ,switch of 5A is not suitable to be used under 1Ma working current .IT is recommended to check the surge current by actual measurement or calculation.IF surge current is too big, problems such as melting will occur even the regular current is small.