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page 1/12 features C ultra-low pressure ranges from 25 to 500 pa (0.1 to 2 inh 2 o) C pressure sensor based on thermal micro- flow measurement C high flow impedance C very low flow-through leakage C high immunity to dust and humidity C no loss in sensitivity using long tubing C outstanding long-term stability and precision with patented real-time ofset compensation and linearization techniques C ofset long term stability better than 0.1 pa/year C total accuracy better than 0.5% fs typical C on-chip temperature sensor C linearized digital spi and analog outputs C small footprint, low profile, only 9 mm in height, and robust package C pressure ports for direct manifold assemblies C highly versatile to fit to application-specific mounting adaptors and manifolds C minimized internal volume and manifold mount option allow for fast gas purge time certificates C quality management system according to en iso 13485 and en iso 9001 C rohs and reach compliant media compatibility air and other non-corrosive gases applications medical C ventilators C spirometers C cpap C sleep diagnostic equipment C nebulizers C oxygen conservers/concentrators C insuflators/endoscopy industrial C hvac C vav C filter monitoring C burner control C fuel cells C gas leak detection C gas metering C fume hood C instrumentation C security systems the lme diferential low pressure sensors are based on thermal flow measurement of gas through a micro-flow channel integrated within the sensor chip. the innovative lme technology features superior sensitivity especially for ultra low pressures. the extremely low gas flow through the sensor ensures high immunity to dust contamination, humidity and long tubing compared to other flow-based pressure sensors. e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 2/12 part no. operating pressure proof pressure (3) burst pressure (3) LMES025U... 0...25 pa / 0...0.25 mbar (0.1 inh 2 o) 2 bar (30 psi) 5 bar (75 psi) lmes050u... 0...50 pa / 0...0.5 mbar (0.2 inh 2 o) lmes100u... 0...100 pa / 0...1 mbar (0.4 inh 2 o) lmes250u... 0...250 pa / 0...2.5 mbar (1 inh 2 o) lmes500u... 0...500 pa / 0...5 mbar (2 inh 2 o) lmes025b... 0...25 pa / 0...0.25 mbar (0.1 inh 2 o) lmes050b... 0...50 pa / 0...0.5 mbar (0.2 inh 2 o) lmes100b... 0...100 pa / 0...1 mbar (0.4 inh 2 o) lmes250b... 0...250 pa / 0...2.5 mbar (1 inh 2 o) lmes500b... 0...500 pa / 0...5 mbar (2 inh 2 o) specification notes (1) sweep 20 to 2000 hz, 8 min, 4 cycles per axis, mil-std-883, method 2007. (2) 5 shocks, 3 axes, mil-std-883e, method 2002.4. (3) the max. common mode pressure is 5 bar. (4) for example with a lmes500... sensor measuring co 2 gas, at full-scale output the actual pressure will be: p ef = p sensor x gas correction factor = 500 pa x 0.56 = 280 pa p ef = true diferential pressure, p sensor = diferential pressure as indicated by output signal pressure sensor characteristics parameter min. max. unit supply voltage v s 4.75 5.25 v dc output current 1 ma lead specifications average preheating temperature gradient 2.5 k/s soak time ca. 3 min time above 217 c 50 s time above 230 c 40 s time above 250 c 15 s peak temperature 260 c cooling temperature gradient -3.5 k/s temperature ranges compensated 0 +70 c operating -20 +80 c storage -40 +80 c humidity limits (non-condensing) 97 %rh vibration (1) 20 g mechanical shock (2) 500 g maximum ratings gas type correction factor dry air 1.0 oxygen (o 2 ) 1.07 nitrogen (n 2 ) 0.97 argon (ar) 0.98 carbon dioxide (co 2 ) 0.56 gas correction factors (4) e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 3/12 performance characteristics (5) (v s =5.0 v dc , t a =20 c, p abs =1 bara, calibrated in air, output signal is non-ratiometric to v s ) 25 pa and 50 pa devices parameter min. typ. max. unit noise level (rms) 0.01 pa ofset warm-up shift less than noise ofset long term stability (6) 0.05 0.1 pa/year ofset repeatability 0.01 pa span repeatability (9, 10) 0.25 % of reading current consumption (no load) (7) 7 8 ma response time (t 63 ) 5 ms power-on time 25 ms digital output parameter min. typ. max. unit scale factor (digital output) (8) 0...25/0...25 pa 1200 counts/pa 0...50/0...50 pa 600 counts/pa zero pressure ofset accuracy (9) 0.1 0.2 %fss span accuracy (9, 10) 0.4 0.75 % of reading thermal efects ofset 5...55 c 0.2 %fss 0...70 c 0.4 %fss span 5...55 c 1 1.75 % of reading 0...70 c 2 2.75 % of reading analog output (unidirectional devices) parameter min. typ. max. unit zero pressure ofset (9) 0.49 0.50 0.51 v full scale output 4.50 v span accuracy (9, 10) 0.4 0.75 % of reading thermal efects ofset 5...55 c 15 mv 0...70 c 30 mv span 5...55 c 1.25 2 % of reading 0...70 c 2 2.75 % of reading analog output (bidirectional devices) parameter min. typ. max. unit zero pressure ofset (9) 2.49 2.50 2.51 v output at max. specified pressure 4.50 v at min. specified pressure 0.50 v span accuracy (9, 10) 0.4 0.75 % of reading thermal efects ofset 5...55 c 15 mv 0...70 c 30 mv span 5...55 c 1.25 2 % of reading 0...70 c 2 2.75 % of reading specification notes (cont.) (5) the sensor is calibrated with a common mode pressure of 1 bar absolute. due to the mass flow based measuring principle, variations in absolute common mode pressure need to be compensated according to the following formula: p ef = p sensor x 1 bara/p abs p ef = true diferential pressure, p sensor = diferential pressure as indicated by output voltage, p abs = current absolute common mode pressure) (6) figure based on accelerated lifetime test of 10000 hours at 85 c biased burn-in. (7) please contact first sensor for low power options. (8) the digital output signal is a signed, two complement integer. negative pressures will result in a negative output (9) zero pressure ofset accuracy and span accuracy are uncorrelated uncertainties. they can be added according to the principles of error propagation. (10) span accuracy below 10% of full scale is limited by the intrinsic noise of the sensor. e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 4/12 performance characteristics (cont.) (5) (v s =5.0 v dc , t a =20 c, p abs =1 bara, calibrated in air, output signal is non-ratiometric to v s ) 100 pa, 250 pa and 500 pa devices parameter min. typ. max. unit noise level (rms) 0.01 %fss ofset warm-up shift less than noise ofset long term stability (6) 0.05 0.1 %fss/year ofset repeatability (11) 0.02 pa span repeatability (9, 10) 0.25 % of reading current consumption (no load) (7) 7 8 ma response time (t 63 ) 5 ms power-on time 25 ms digital output parameter min. typ. max. unit scale factor (digital output) (8) 0...100/0...100 pa 300 counts/pa 0...250/0...250 pa 120 counts/pa 0...500/0...500 pa 60 counts/pa zero pressure ofset accuracy (9) 0.05 0.1 %fss span accuracy (9, 10) 0.4 0.75 % of reading thermal efects ofset 5...55 c 0.1 %fss 0...70 c 0.2 %fss span 5...55 c 1 1.75 % of reading 0...70 c 2 2.75 % of reading analog output (unidirectional devices) parameter min. typ. max. unit zero pressure ofset (9) 0.49 0.50 0.51 v full scale output 4.50 v span accuracy (9, 10) 0.4 0.75 % of reading thermal efects ofset 5...55 c 10 mv 0...70 c 12 mv span 5...55 c 1 1.75 % of reading 0...70 c 2 2.75 % of reading analog output (bidirectional devices) parameter min. typ. max. unit zero pressure ofset (9) 2.49 2.50 2.51 v output at max. specified pressure 4.50 v at min. specified pressure 0.50 v span accuracy (9, 10) 0.4 0.75 % of reading thermal efects ofset 5...55 c 10 mv 0...70 c 12 mv span 5...55 c 1 1.75 % of reading 0...70 c 2 2.75 % of reading specification notes (cont.) (5) the sensor is calibrated with a common mode pressure of 1 bar absolute. due to the mass flow based measuring principle, variations in absolute common mode pressure need to be compensated according to the following formula: p ef = p sensor x 1 bara/p abs p ef = true diferential pressure, p sensor = diferential pressure as indicated by output voltage, p abs = current absolute common mode pressure) (6) figure based on accelerated lifetime test of 10000 hours at 85 c biased burn-in. (7) please contact first sensor for low power options. (8) the digital output signal is a signed, two complement integer. negative pressures will result in a negative output (9) zero pressure ofset accuracy and span accuracy are uncorrelated uncertainties. they can be added according to the principles of error propagation. (10) span accuracy below 10% of full scale is limited by the intrinsic noise of the sensor. (11) typical value for 250 pa sensors. e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 5/12 performance characteristics (cont.) total accuracy (12) total error [ %fs ] pressure [pa] specification notes (cont.) (12) total accuracy is the combined error from ofset and span calibration, non-linearity, repeatability and pressure hysteresis ofset long term stability fig. 2: ofset long term stability for lme 250 pa sensors after 10,000 hours @ 85c powered, equivalent to over 43.5 years @ 25 c (better than 2 mv / 0.125 pa) time [h] analog output [ v ] fig. 1: typical total accuracy plot of 16 lme 50 pa sensors @ 25 c (typical total accuracy better than 0.5 %fs) temperature sensor parameter min. typ. max. unit scale factor (digital output) 95 counts/c non-linearity 0.5 %fs hysteresis 0.1 % fs e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 6/12 spi C serial peripheral interface introduction the lme serial interface is a high-speed synchronous data input and output communication port. the serial interface operates using a stan - dard 4-wire spi bus. the lme device runs in spi mode 0, which requires the clock line sclk to idle low (cpol = 0), and for data to be sampled on the leading clock edge (cpha = 0). figure 5 illustrates this mode of operation. care should be taken to ensure that the sensor is properly connected to the master microcontroller. refer to the manufacturer's datasheet for more information regarding physical connections. application circuit the use of pull-up resistors is generally unnecessary for spi as most master devices are configured for push-pull mode. there are, however, some cases where it may be helpful to use 33 ? series resistors at both ends of the spi lines, as shown in figure 3. signal quality may be further improved by the addition of a bufer as shown in figure 4. these cases include multiple slave devices on the same bus segment, using a master device with limited driving capability and long spi bus lines. if these series resistors are used, they must be physically placed as close as possible to the pins of the master and slave devices. signal control the serial interface is enabled by asserting /cs low. the serial input clock, sclk, is gated internally to begin accepting the input data at mosi, or sending the output data on miso. when /cs rises, the data clocked into mosi is loaded into an internal register. mosi miso sclk /cs c 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? fig. 3: application circuit with resistors at both ends of the spi lines fig. 4: application circuit with additional bufer sensor 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? 33 ? /oe /oe /oe /oe mosi miso sclk /cs mosi miso sclk /cs c sensor mosi miso sclk /cs e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 7/12 spi C serial peripheral interface (cont.) data read C pressure when powered on, the sensor begins to continuously measure pressure. to initiate data transfer from the sensor, the following three unique bytes must be written sequentially, msb first, to the mosi pin (see figure 5): the entire 16 bit content of the lme register is then read out on the miso pin, msb first, by applying 16 successive clock pulses to sclk with /cs asserted low. note that the value of the lsb is held at zero for internal signal processing purposes. this is below the noise threshold of the sensor and thus its fixed value does not afect sensor performance and accuracy. from the digital sensor output the actual pressure value can be calculated as follows: for example, for a 250 pa sensor (lmes250b...) with a scale factor of 120 a digital output of 30 000 counts (7530h) calculates to a positive pressure of 250 pa. similarly, a digital output of -30 000 counts (8ad0h) calculates to a negative pressure of -250 pa. step hexadecimal binary description 1 0x2d b00101101 poll current pressure measurement 2 0x14 b00010100 send result to data register 3 0x98 b10011000 read data register pressure [pa] = digital output [counts] scale factor [ counts ] pa 0 1 0 1 1 1 0 0 0 1 0 1 0 0 0 0 1 0 1 1 0 0 0 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 fig. 5: spi data transfer mosi miso sclk (cpol=0) (cpha=0) /cs step 1 step 2 step 3 data from sensor mosi miso sclk (cpol=0) (cpha=0) /cs msb lsb e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 8/12 spi C serial peripheral interface (cont.) data read C temperature the on-chip temperature sensor changes +95 counts/c over the operating range. the temperature data format is 15-bit plus sign in twos complement format. to read temperature, use the following sequence: step hexadecimal binary description 1 0x24 b00100010 poll current temperature measurement 2 0x14 b00010100 send result to data register 3 0x98 b10011000 read data register from the digital sensor output, the actual temperature can be calculated as follows: temperature [c] = ts - ts 0 [counts] + t 0 [c] scale factor ts [ counts ] c where ts is the actual sensor readout; ts 0 is the sensor readout at known temperature t 0 (13) ; scale factor ts = 95 counts/c specification notes (cont.) (13) to be defined by user. the results show deviation (in c) from the ofset calibrated temperature. e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 9/12 parameter symbol conditions min. typ. max. unit external clock frequency f eclk v cksel =0 min. 0.2 mhz max. 5 external master clock input low time f eclkin lo t eclk =1/f eclk 40 60 %t eclk external master clock input high time f eclkin hi t eclk =1/f eclk 40 60 sclk setup to falling edge /cs t sc 30 ns /cs falling edge to sclk rising edge setup time t css 30 /cs idle time t csi f clk =4 mhz 1.5 s sclk falling edge to data valid delay t do c load =15 pf 80 ns data valid to sclk rising edge setup time t ds 30 data valid to sclk rising edge hold time t dh 30 sclk high pulse width t ch 100 sclk low pulse width t cl 100 /cs rising edge to sclk rising edge hold time t csh 30 /cs falling edge to output enable t dv c load =15 pf 25 /cs rising edge to output disable t tr c load =15 pf 25 maximum output load capacitance c load r load = f , phase margin >55 200 pf input voltage, logic high v ih 0.8v s v s +0.3 v input voltage, logic low v il 0.2v s output voltage, logic high v oh r load = f v s -0.1 r load =2 k : v s -0.15 output voltage, logic low v ol r load = f 0.5 r load =2 k : 0.2 spi C serial peripheral interface (cont.) interface specification fig. 6: spi timing diagram mosi miso sclk /cs t css t sc t ch t cl t csh t csi t ds t dh t dv t do t tr e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 10/12 electrical connection pin function case 1: digital signal output case 2: analog signal output 1 v s +5v +5v 2 gnd gnd gnd 3 vout nc high impedance analog input (e.g. op-amp, adc) 4 reserved nc nc 5 sclk master device sclk gnd 6 mosi master device mosi gnd 7 miso master device miso gnd 8 /cs master device (/cs) v s there are two use cases that will change the manner in which the lme series device is connected in-circuit: 1 2 3 4 8 7 6 5 dimensional drawing dimensions in mm, all tolerances 0.1 mm unless otherwise noted e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 11/12 manifold diagram for two side-by-side mounted sensors recommended o-rings: part number: 90025k119 www.mcmaster.com manifold diagram for multiple side-by-side mounted sensors dimensions in mm, all tolerances 0.1 mm unless otherwise noted e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com
page 12/12 ordering information gas mixture change (purge time) the lme series pressure sensors feature minimized internal volume, which allows for fast response to gas mixture change and high pneumatic impedance at the same time. purge time (t p ) can be estimated by the following equation: t p = purge time [s] v int = internal volume of the lme sensor [ml] t p = v int = v int f norm p norm /z p f nom = nominal flow [ml/s] p nom = nominal pressure [pa] z p = pneumatic impedance [kpa/(ml/s)] the typical internal volume of the lme sensor (v int ) is 0.04 ml. with a pneumatic impedance (z p ) of 15 kpa/(ml/s) and a nominal pressure (p nom ) of 250 pa, the estimated purge time (t p ) is 2.4 seconds. series pressure range calibration housing output grade lme s025 25 pa (0.1 inh 2 o) b bidirectional b [smd, 2 ports, axial, same side] 6 [non-ratiometric, 5 v supply] s [high] s050 50 pa (0.2 inh 2 o) u unidirectional s100 100 pa (0.4 inh 2 o) s250 250 pa (1 inh 2 o) s500 500 pa (2 inh 2 o) custom adaptor the lme series pressure sensors can optionally be equipped with a custom adaptor for your application-specific mounting requirements. please contact first sensor for more information. fig. 7: 3d views of a custom adaptor for the lme pressure sensor e / 11822 / c lme series C digital low diferential pressure sensors subject to change without notice www.first-sensor.com contact@first-sensor.com

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