WBI Series Mass flow sensors for gases FEATURES · Flow ranges 0...200 sccm, 0...±200 sccm, 0...1 slpm, 0...±1 slpm · Thermal mass flow sensing · Digital I²C bus output · RoHS and REACH compliant · Quality Management System according to ISO 13485:2003 and ISO 9001:2008 MEDIA COMPATIBILITY7 To be used with dry gases only. The WBI series is NOT designed for liquid flow and will be damaged by liquid flow through the sensor. SPECIFICATIONS6 ELECTRICAL CONNECTION Maximum ratings Supply voltage 2.7 ... 5.5 V Temperature limits Compensated Operating Storage 0 ... 50 °C -25 ... 85 °C -40 ... 125 °C Humidity limits (non-condensing) 0 ... 95 %RH Vibration1 20 g 2 Mechanical shock 30 g Pin Connection 2 SD A 3 I / C* 4 +Vs 5 GND 6 SC L * Internal connection. Do not connect for any reason E / 11354 / H 1/7 www.first-sensor.com www.sensortechnics.com WBI Series Mass flow sensors for gases FLOW SENSOR CHARACTERISTICS7 (VS = 5 ±0.01 V, TA = 20 °C, PAbs= 101.325 kPa) Part no. WBIM200DU... WBIM200DB... WBIL001DU... WBIL001DB... Flow range 0...200 sccm 0...±200 sccm 0...1 slpm 0...±1 slpm Max. flow ch an g e Pressure drop Max. Common mode pressure 5.0 slpm/sec 0.1 mbar @ 200 sccm 0.5 mbar @ 1 slpm 2 5 p si Note: sccm denotes standard cubic centimeters per minute. slpm denotes standard liter per minute. PERFORMANCE CHARACTERISTICS6 (VS = 5 ±0.01 V, TA = 20 °C, PAbs= 101.325 kPa, output signal is ratiometric to VS, media = air) Characteristics Min. Typ. Accuracy3 Total accuracy (0...50 °C)4 Repeatability (incl. hysteresis) Offset long term stability (1 year) Noise level Current consumption (no load) Response time (t90) Warm-up time8 Max. Unit ±(2.0 % of reading + 0.25 %FSO) ±(4.0 % of reading + 0.25 %FSO) 0.25 % of reading ±0.05 10 0.1 12 5 70 %FSS mA ms Digital output Characteristics Scale factor Zero offset tolerance Full scale span tolerance Min. WBIM200... WBIL001... Typ. Max. 150 30 Unit counts/sccm ±0.25 ±2.25 % FS S Note: The sensor’s performance is determined by intake flow conditions which depend on mounting and environmental effects. To ensure laminar flow through the sensor, it should be considered to insert a straight tube with a length 10 times the inner diameter of the pneumatic connector or a laminar flow element upstream of the sensor. Additionally, the WBI has to be mounted with both ports horizontally and pins downwards. E / 11354 / H 2/7 www.first-sensor.com www.sensortechnics.com WBI Series Mass flow sensors for gases DIGITAL I²C BUS The WBI complies with the following protocol (Fig. 1): (according to the read/write bit it sent), and the slave continues in its complementary mode (receive or transmit, respectively). Bus idle (A): Both the series data line and the series clock line are HIGH. START condition (B): When SCL is HIGH, a change of SDA from HIGH to LOW represents a start condition that initiates data transfer. A start condition must present before any data transfer commands can be executed. STOP condition (C): When SCL is HIGH, a change of SDA from LOW to HIGH represents a stop condition that ceases data transfer. All the data transfer commands must be accomplished before a stop condition presents. DATA (D): After the start condition, the series data line must be kept steady when the series clock line is HIGH. The series data line can change during the period when the series clock line is LOW, and each data bit must correspond to a clock pulse. Slave address: The I²C-bus master-slave concept requires a unique address for each device on the bus. The WBI has a reserved address (00h) for broadcasting and a second individual address preconfigured to 01h. The sensor will listen to both slave addresses. 00h can only be used for WRITE commands. By programming it is possible to reset the individual adress to any number between 1 and 127 (see Comands). After generating a START condition the master sends the address byte containing a 7 bit address followed by a data direction bit (R/W). A "0" indicates a transmission from master to slave (WRITE), a "1" indicates a data request (READ). DATA operation: The address and the data bytes are sent most significant bit first. Each data transfer will begin with a start condition and cease after a stop condition. Every byte put on the series data line must be 8 bits long. The number of bytes that can be transmitted per transfer is unrestricted. Each byte has to be followed by an Acknowledge/not Acknowledge bit. The number of data bytes between a start condition and a stop condition will be decided by the bus master. If the master wishes to write into the slave then it repeatedly sends a byte with the slave sending an ACK bit. (In this situation, the master is in the master transmit mode and the slave is in the slave receive mode.) If the master wishes to read from the slave then it repeatedly receives a byte from the slave, the master sending an ACK bit after every byte but the last one. (In this situation, the master is in the master receive mode and the slave is in the slave transmit mode.) Acknowledge bit: The master is initially in the master transmit mode by sending a start bit followed by the slave address that it wishes to communicate with, which is finally followed by a single bit representing whether it wishes to write(0) to or read(1) from the slave. If the slave exists on the bus then it will respond with acknowledge (ACK) bit (active low for acknowledged) for that address. The master must provide an extra SCL pulse for each ACK bit. The master then continues in either transmit or receive mode (A) (B) (D) The master then ends transmission with a stop bit, or it may send another start bit if it wishes to retain control of the bus for another transfer (a "combined message"). Note: The WBI sensor can hold SCL LOW after each data byte before ACK. The transaction cannot continue until SCL is HIGH again and therefore the master has to wait. (D) (D) (C) (A) SCL SDA START condition Fig. 1: Data valid Data allowed to change STOP condition I²C bus protocol E / 11354 / H 3/7 www.first-sensor.com www.sensortechnics.com WBI Series Mass flow sensors for gases DIGITAL I²C BUS (cont.) Commands: The WBI series flow sensors use a communication mode based on the command interpretation mechanism. The data accesses are accomplished through various commands (Fig. 2): Read instant flow index 0 1 S slave address R/W A 83h A S slave address R/W A data byte 1 A data byte 2 A data byte 3 A data byte 4 A P This command is used for enquiring the current instant flow index. The index consists of four 8-bit values, which are combined to give a 32-bit value as follows: Flow index = (data byte 1× 16777216 ) + (data byte 2 × 65536 ) + (data byte 3 × 256 ) + (data byte 4 ) The actual flow value can be calculated as the following: Actual flow value = flow index scale factor × 1000 Negative numbers are represented by the two's complement. Example for WBIM200DBH5: Sensor output = FF FE 1D C0 Flow index = -123456 Actual flow value = −123456 = − 0.823 sccm 150 × 1000 Read I²C address 0 1 S slave address R/W A 85h A S slave address R/W A slave address 0 A P Write I²C address 0 S slave address R/W A 05h A new slave address 0 A P Auto zero 0 S slave address R/W A 1Ch A 00h A P generated by master S = START condition generated by slave A = Acknowledge P = STOP condition Fig. 2: WBI commands E / 11354 / H 4/7 www.first-sensor.com www.sensortechnics.com WBI Series Mass flow sensors for gases DIGITAL I²C BUS (cont.) I²C Interface Parameters Parameter Symbol Input high level Input low level Output low level Pull-up resistor Load capacitance @ SDA Input capacitance @ SDA/SCL SCL clock frequency Bus free time between STOP and START condition Hold time (repeated) START condition, to first clock pulse LOW period of SCL HIGH period of SCL Setup time repeated START condition Data hold time Data setup time Rise time of both SDA and SCL Fall time of both SDA and SCL Setup time for STOP condition tSU;DAT tHD;DAT Min. Typ. 90 0 Max. Unit 100 10 10 % of V s 10 C SD A CI2C_IN FSC L tBUF tHD.STA tLOW tHIGH tSU.STA tHD.DAT tSU.DAT tR tF tSU.STO kΩ 400 10 100 4.7 4.7 4.7 4.0 4.7 0 0.25 pF kHz µs 1 0.3 4 tSU;STA tHD;STA tR tSU;STO tBUF tHD;STA tF SCL SDA tHIGH tLOW SCL SDA Fig. 3: Timing characteristics E / 11354 / H 5/7 www.first-sensor.com www.sensortechnics.com WBI Series Mass flow sensors for gases OUTLINE DRAWING Note: Positive flow direction is defined as proceeding from P1 to P2 and results in positive output. third angle projection dimensions in mm E / 11354 / H 6/7 www.first-sensor.com www.sensortechnics.com WBI Series Mass flow sensors for gases GAS CORRECTION FACTORS9 Gas type Ai r Oxygen (O2) Nitrogen (N2) Argon (Ar) Hydrogen (H2) Carbon dioxide (CO2) Gas correction factor 1.0 1.0 1.0 1.18 * 0.67 * For Hydrogen applications, the actual H2 calibration is performed whenever possible. Specification notes: 1. 2. 3. 4. 5. 6. 7. 8. 9. Sweep 20 to 2000 Hz, 8 min, 4 cycles per axis, MIL-STD-883, Method 2007. 5 shocks, 3 axes, MIL-STD-883E, Method 2002.4. Accuracy is the combined error from offset and span calibration, linearity, hysteresis and repeatability. Total accuracy is the combined error from offset and span calibration, linearity, hysteresis, repeatability and temperature effects. Full Scale Span (FSS) is the algebraic difference between the output signal for the highest and lowest specified flow. Specification is preliminary. Data sheet is based on Pre-Series sample verification. A 5 µm filter is recommended to protect the sensing element from dust particles which may be present in some applications. Warm-up time is the time from power on to the first stable reading. To obtain the real flow rates in a specific gas, multiply the readings from the sensor by the gas correction factor in the table. The factors are approximate and should be used as guidelines only. Sensor performance strongly depends on gas dynamics and has to be evaluated in the respective application. ORDERING INFORMATION Series Options WBI Flow range Gas Flow direction M200 200 sccm D* Dry air B Bidirectional L 001 U Unidirectional 1 slpm Grade H High Calibration 5 5V (VS=2.7...5.5 V) * other calibration gases on request Example: WBI M200 D U H 5 First Sensor reserves the right to make changes to any products herein. First Sensor does not assume any liability arising out of the application or use of any product or circuit described herein, neither does it convey any license under its patent rights nor the rights of others. E / 11354 / H 7/7 www.first-sensor.com www.sensortechnics.com