1 motorola sensor device data
prepared by: jc hamelain toulouse pressure sensor laboratory semiconductor products sector, toulouse, france introduction motorola discrete products provides a complete solution for designing a low cost system for direct and accurate liquid level control using an ac powered pump or solenoid valve. this circuit approach which exclusively uses motorola semiconductor parts, incorporates a piezoresistive pressure sensor with onchip temperature compensation and a new solidstate relay with an integrated power triac, to drive directly the liquid level control equipment from the domestic 110/220 v 50/60 hz ac main power line. pressure sensor description the mpxm2000 series pressure sensor integrates onchip, lasertrimmed resistors for offset calibration and temperature compensation. the pressure sensitive element is a patented, single piezoresistive implant which replaces the four resistor wheatstone bridge traditionally used by most pressure sensor manufacturers. mpak axial port case 1320a depending on the application and pressure range, the sensor may be chosen from the following portfolio. for this application the mpxm2010gs was selected. device pressure range application sensitivity* mpxm2010gs 0 to 10 kpa 0.01 kpa (1 mm h 2 o) mpxm2053gs 0 to 50 kpa 0.05 kpa (5 mm h 2 o) mpxm2102gs 0 to 100 kpa 0.1 kpa (10 mm h 2 o) mpxm2202gs 0 to 200 kpa 0.2 kpa (20 mm h 2 o) * after proper gain adjustment pin 3 r s1 r p xducer r off1 pin 2 pin 4 + v out v out laser trimmed onchip r s2 pin 1 r off2 + v s r1 r2 figure 1. pressure sensor mpxm2000 series power opto is a trademark of motorola inc. order this document by AN1516/d
semiconductor application note ? motorola, inc. 2002 rev 2 f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
2 motorola sensor device data power opto isolator moc2a60 description the moc2a60 is a new motorola power opto ? isolator and consists of a gallium arsenide, infrared emitting diode, which is optically coupled to a zerocross triac driver and a power triac. it is capable of driving a load of up to 2 a (rms) directly from a line voltage of 220 v (50/60 hz). zva * device schematic 1, 4, 5, 6, 8. no pin 1, 4, 5, 6, 2. led cathode 1, 4, 5, 6, 3. led anode 1, 4, 5, 6, 7. main terminal 1, 4, 5, 6, 9. main terminal * zero voltage activate circuit 9 7 3 2 case 417 plastic package figure 2. moc2a60 power opto isolator signal conditioning when a full range pressure is applied to the mpxm2010gs, it will provide an output of about 20 mv (at an 8 v supply). therefore, for an application using only a few percent of the pressure range, the available signal may be as low as a few hundred microvolts. to be useful, the sensor signal must be amplified. this is achieved via a true differential amplifier (a1 and a2) as shown in figure 4. the gain adj (500 ohm) resistor, r g , sets the gain to about 200. the differential output of this stage is amplified by a second stage (a3) with a variable offset resistor. this stage performs a differential to singleended output conversion and references this output to the adjustable offset voltage. this output is then compared to a voltage (v ref = 4 v at tp2) at the input of the third stage (a4). this last amplifier is used as an inverted comparator amplifier with hysteresis (schmitt trigger) which provides a logic signal (tp3) within a preset range variation of about 10% of the input (selected by the ratio r9/(r9 + r7). if the pressure sensor delivers a voltage to the input of the schmitt trigger (pin 13) lower than the reference voltage (pin 12), then the output voltage (pin 14) is high and the drive current for the power stage moc2a60 is provided. when the sensor output increases above the reference voltage, the output at pin 14 goes low and no drive current is available. the amplifier used is a motorola mc33179. this is a quad amplifier with large current output drive capability (more than 80 ma). output power stage for safety reasons, it is important to prevent any direct contact between the ac main power line and the liquid environment or the tank. in order to maintain full isolation between the sensor circuitry and the main power, the solidstate relay is placed between the low voltage circuit (sensor and amplifier) and the ac power line used by the pump and compressor. the output of the last stage of the mc33179 is used as a current source to drive the led (light emitting diode). the series resistor, r8, limits the current into the led to approximately 15 ma and guarantees an optimum drive for the power optotriac. the ld1 (mfoe76), which is an infrared light emitting diode, is used as an indicator to detect when the load is under power. the moc2a60 works like a switch to turn on or off the pump's power source. this device can drive up to 2 a for an ac load and is perfectly suited for the medium power motors (less than 500 watts) used in many applications. it consists of an optotriac driving a power triac and has a zerocrossing detection to limit the power line disturbance problems when fast switching selfic loads. an rc network, placed in parallel with the output of the solidstate relay is not required, but it is good design practice for managing large voltage spikes coming from the inductive load commutation. the load itself (motor or solenoid valve) is connected in series with the solidstate relay to the main power line. example of application: accurate liquid level monitoring the purpose of the described application is to provide an electronic system which maintains a constant liquid level in a tank (within 5 mm h 2 o). the liquid level is kept constant in the tank by an ac electric pump and a pressure sensor which provides the feedback information. the tank may be of any size. the application is not affected by the volume of the tank but only by the difference in the liquid level. of course, the maximum level in the tank must correspond to a pressure within the operating range of the pressure sensor. liquid level sensors motorola has developed a piezoresistive pressure sensor family which is very well adapted for level sensing, especially when using an air pipe sensing method. these devices may also be used with a bubbling method or equivalent. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
3 motorola sensor device data open pipe before calibration control module pressure sensor air liquid level in the pipe electrical pump ac line reference level h figure 3. liquid level monitoring level sensing theory if a pipe is placed vertically, with one end dipped into a liquid and the other end opened, the level in the pipe will be exactly the same as the level in the tank. however, if the upper end of the pipe is closed off and some air volume is trapped, the pressure in the pipe will vary proportionally with the liquid level change in the tank. for example, if we assume that the liquid is water and that the water level rises in the tank by 10 mm, then the pressure in the pipe will increase by that same value (10 mm of water). a gauge pressure sensor has one side connected to the pipe (pressure side) and the other side open to ambient (in this case, atmospheric) pressure. the pressure difference which corresponds to the change in the tank level is measured by the pressure sensor. pressure sensor choice in this example, a level sensing of 10 mm of water is desired. the equivalent pressure in kilo pascals is 0.09806 kpa. in this case, motorola's temperature compensated 0 10 kpa, mpxm2010gs is an excellent choice. the sensor output, with a pressure of 0.09806 kpa applied, will result in 2.0 mv/kpa x 0.09806 = 0.196 mv. the sensing system is designed with an amplifier gain of about 1000. thus, the conditioned signal voltage given by the module is 1000 x 0.196 mv = 0.196 v with 10 mm h 2 o pressure. table 1. liquid level sensors method sensor advantage disadvantages liquid weight magnetoresitive low power, no active electronic low resolution, range limited magnetoresitive very high resolution complex electronic ultrasonic easy to install need high power, low accuracy liquid resistivity no active electronic no active electronic low resolution, liquid dependent string potentiometer potentiometer low power, no active electronic poor linearity, corrosion pressure silicon sensors inexpensive good resolution, wide range measurements active electronic, need power f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
4 motorola sensor device data rg = 500 w r1, r2 = 100 k r5, r7 = 100 k r3, r4 . . . r6 = 10 k r9 . . . r11 = 10 k r8 = 100 r off = 25 k var a1 . . . a4 = 1/4 mc33179 d1 = mled76 mc7808ac = regl 8 vdc tr = transformer 220:12 v c1 = 40 m f 40 v offset adjust reference adj r off r10 r11 r9 r7 r3 r4 r2 r1 rg 32 4 1 5 6 + a2 a1 2 1 3+ 4 7 11 gain adj + + 10 9 8 tp1 tp2 + 12 13 a3 a4 14 tp3 r6 r8 d1 r c motor n p l tr 220 vac +8 vdc c1 mpxm2010gs r5 mc78l08 moc2a60 figure 4. electrical circuit liquid level pressure sensing (tp1) trigger voltage (tp3) pump voltage (ac220v) max min 7 v 0 4.3 v 0.4 v ref (tp2) 3.7 v sensing for minimum level (pumping into the tank) the sensing probe is tied to the positive pressure port of the sensor. the pump is turned on to fill the tank when the minimum level is reached. figure 5. functional diagram 10 mm f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
5 motorola sensor device data level control modes this application describes two ways to keep the liquid level constant in the tank; first, by pumping the water out if the liquid level rises above the reference, or second, by pumping the water in if the liquid level drops below the reference. if pumping water out, the pump must be off when the liquid level is below the reference level. to turn the pump on, the sensor signal must be decreased to drop the input to the schmitt trigger below the reference voltage. to do this, the sensing pipe must be connected to the negative pressure port (back or vacuum side) of the sensor. in the condition when the pressure increases (liquid level rises), the sensor voltage will decrease and the pump will turn on when the sensor output crosses the referenced level. as pumping continues, the level in the tank decreases (thus the pressure on the sensor decreases) and the sensor signal increases back up to the trigger point where the pump was turned off. in the case of pumping water into the tank, the pump must be off when the liquid level is above the reference level. to turn on the pump, the sensor signal must be decreased to drive the input schmitt trigger below the reference voltage. to do this, the sensing pipe must be connected to the positive pressure port (top side) of the sensor. in this configuration when the pressure on the sensor decreases, (liquid level drops) the sensor voltage also decreases and the pump is turned on when the signal exceeds the reference. as pumping continues, the water level increases and when the maximum level is reached, the schmitt trigger turns the pump off. adjustments the sensing tube is placed into the water at a distance below the minimum limit level anywhere in the tank. the other end of the tube is opened to atmosphere. when the tank is filled to the desired maximum (or minimum) level, the pressure sensor is connected to the tube with the desired port configuration for the application. then the water level in the tank is the reference. after connecting the tube to the pressure sensor, the module must be adjusted to control the water level. the output voltage at tp1 is preadjusted to about 4 v (half of the supply voltage). when the sensor is connected to the tube, the module output is on (lighted) or off. by adjusting the offset adjust potentiometer the output is just turned into the other state: off, if it was on or the reverse, on, if it was off, (the change in the tank level may be simulated by moving the sensing tube up or down). the reference point tp2 shows the on/off reference voltage, and the switching point of the module is reached when the voltage at tp1 just crosses the value of the tp2 voltage. the module is designed for about 10 mm of difference level between on and off (hysteresis). conclusion this circuit design concept may be used to evaluate motorola pressure sensors used as a liquid level switch. this basic circuit may be easily modified to provide an analog signal of the level within the controlled range. it may also be easily modified to provide tighter level control ( 2 mm h 2 o) by increasing the gain of the first amplifier stage (decreasing rg resistor). the circuit is also a useful tool to evaluate the performance of the power optocoupler moc2a60 when driving ac loads directly. f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
6 motorola sensor device data notes f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
7 motorola sensor device data notes f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
8 motorola sensor device data motorola reserves the right to make changes without further notice to any products herein. motorola makes no warranty, represen tation, or guarantee regarding the suitability of its products for any particular purpose, nor does motorola assume any liability arising out of the applicati on or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. atypicalo param eters can and do vary in different applications and actual performance may vary over time. all operating parameters, including atypicalso, must be validated for e ach customer application by customer's technical experts. motorola does not convey any license under its patent rights nor the rights of others. motorola p roducts are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to s upport or sustain life, or for any other application in which the failure of the motorola product could create a situation where personal injury or death may occur. sho uld buyer purchase or use motorola products for any such unintended or unauthorized application, buyer shall indemnify and hold motorola and its officers, employe es, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly o r indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that motorola was negligent reg arding the design or manufacture of the part. motorola and the stylized m logo are registered in the us patent & trademark office. all other product or service names are the property of their respective owners. motorola, inc. is an equal opportunity/affirmative action employer. motorola, inc. 2002. how to reach us: usa / europe / locations not listed : motorola literature distribution; p.o. box 5405, denver, colorado 80217. 13036752140 or 18004412447 japan : motorola japan ltd.; sps, technical information center, 3201, minamiaz abu. minatoku, tokyo 1068573 japan. 8 1334403569 asia / pacific : motorola semiconductors h.k. ltd.; silicon harbour centre, 2 dai king street, tai po industrial estate, tai po, n.t. hong kon g. 85226668334 technical information center: 18005216274 home page : http://www.motorola.com/semiconductors/ AN1516/d ? f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
|
