GRUNDFOS DIRECT SENSORS Flow Measurement

Transcription

1 GRUNDFOS DIRECT SENSORS Flow Measurement Application Specification Functionality Validation Options I II III IV V Direct Sensors VFS 1-20, 2-40, 5-100

2 I. Application The Vortex Flow Sensors are combined flow- and temperature transmitters with the intended use in a domestic hot water circuit. The sensor is intended to be used on the secondary heat exchanger side. The flowsensors are now available in a series ranging from litre/minute and 2-40, and The measurement of temperature is always C. The flow signal is to be used for Control of three-way valve Control of burner (required power estimated from DHW flow rate) The integrated temperature signal is to be used for Control of burner (burner power regulated according to actual DHW temperature) Elimination of solitude temperature sensor All Grundfos Direct Sensors are coated with a proprietary and extremely durable coating enabling accurate, cost-effective and robust piezo-resistive sensors. More in section II and IV. The benefits in a boiler derived from using a pressure sensor in conjunction with a flow sensor is described in the Application Note for Pressure Measurement. 2 of 17

3 Application 1 Application 2 CHF CHF Gas valve Heat exchanger VFS 1-20 CHR CHF CHF Gas valve Heat exchanger CHR Temperature sensor VFS 1-20 DHW DCW DHW DCW Boiler control Boiler control Grundfos flow and temperature sensor on the hot water side Grundfos flow and temperature sensor on the cold water side Benefits: Benefits: - measuring both DHW flow and - fits into existing boiler design temperature - possible to combine with stand-alone - cost-effective integration of temperature sensor. two functions in one for domestic hot water efficiency. 3 of 17

4 Temperature (DHW) Setpoint Flow sensor alone Temperature sensor alone Combined flow and temperature sensor Time With a stand-alone temperature sensor a slow and fluctuating regulation of the DHW temperature is obtained. The boiler is able to compensate for changes in inlet DCW temperature, and changes in the efficiency of the heat exchanger, but not with the consumption/flow of water. With a stand-alone flow sensor a fast regulation is obtained, but the temperature of the water is usually lower than required to reduce the risk of scoldering. By combining the two - the best of both worlds will occur: A fast and accurate regulation of the DHW temperature. The Grundfos combined flow and temperature sensor is designed and validated for use on the hot side of the secondary heat exchanger. 4 of 17

5 II. Specifications Coating Specifications Grundfos Direct Sensors Coating Engineering Data for CrTa alloy Hardness 16 GPa Elasticity (Youngs modulus) 180 GPa Tensile Stress (Yield Strength) 6.1 GPa Wear Resistance 0.5 * Nm meter -3 (800% more than Si) Coefficient of linear thermal expansion 7.3 *10-6 K -1 Temperature of Crystallisation > 1070 K Corrosion Rates in ph 11, 100 C μm p.a. Activation Energy for corrosion in ph ev Sensor Specifications Grundfos Direct Sensors Vortex Flow Sensor Sensor Performance (with +/- one std. deviation) Measuring range litre / minute 2 40 litre / minute litre / minute Accuracy, Flow ± 1.5% FS in full temperature range (0 100 C) Response time, Flow < 1 s (63.2% response to step) Measuring range, Temperature C Accuracy, Temperature, ±1 C in operating temperature range (25 C to 80 C) Accuracy, Temperature, ±2 C in full temperature range (0 100 C) Response time, Temperature < 2 s (63.2% response to step) Electrical Interface Supply 5 V DC (±5%), PELV Output signals Ratiometric, i.e. proportional to supply Flow signal 0.35 V 3.5 V proportional to min. max. l/min 1 Temperature signal 0.5 V 3.5 V proportional to C Pin configuration See drawings on following pages Recommended female FCI, p/n , connector fciconnect.com Mechanical Dimensions H*W*D 47*40*20 mm See drawings on following pages Media Temperature Conditions Minimum water temperature 0 C / 32 F (sensor operating) Maximum water temperature 110 C / 230 F (sensor operating) Minimum water temperature -25 C / -13 F (sensor survives) Peak temperature 120 C / 248 F (sensor survives) Media Pressure Conditions Maximum Continuous System Pressure 10 bars / 145 psi (relative) Maximum Pressure Leak Test 15 bars/ 218psi (relative) for 5 min. Ambient Conditions (inside heater cabinet) Minimum Air Temperature -25 C / -13 F Maximum Continuous Air 60 C / 140 F Temperature Peak Air Temperature 90 C / 194 F Protection Enclosure IP 44 1 Q = 1 l/min + [(U-0.5) V / 3.0 V] * 19 l/min 5 of 17

6 Outputs Influence of supply voltage on output signals In relation to the diagram on connections on the following page, please note the following. The sensor is designed to deliver ratiometric signals. This means, that the output signal will change in proportion with the supply voltage for constant temperature or flow, as seen from the above diagrams. An onboard microprocessor is calibrated individually for each sensor to deliver a linearized signal of the flow and temperature. Ratiometric output enables a higher accuracy and lower system cost in applications, where the sensor is connected to an A/D converter using the supply voltage as reference voltage. The diagram on the following page illustrates the recommended connection of the sensor to a boiler control. To avoid unintended intrusion of water, it is recommended to mount the sensor upside down. 6 of 17

7 Connections between sensor and boiler control 7 of 17

8 Mechanical Dimensions and Pin configuration Dimensions around sensor fastening to flowpipe Sensor body dimensions and plug schematics Pin Configuration 8 of 17

9 Built in Directives d D flow direction L X L1 flow direction Standard Flowsensors (incl. pipes etc.) supplied by Grundfos. Parameter Symbol Value in units of Value for VFS 1-20 Value for VFS 2-40 Value for VFS pipe diameter (D) Pipe diameter D - 10 mm 12 mm 18mm Distance to L 1 4D 40 mm 48 mm 72 mm nearest upstream bend Upstream edge of X 1.5D 15 mm 18 mm 27 mm vortex generator to sensor centerline Length of vortex L 0.55D 5.5 mm 6.6 mm 9.9 mm generator Width of vortex d 0.33D 3.3 mm 4.0 mm 5.9 mm generator ½" (clip) 5/8" / 3/4" (clip) 1" thread Connections mm (pipe) + 72,5 mm (fitting) 88 mm (pipe) + 50mm (fitting) of 17

10 III. Functionality Theory of operation The Vortex Flow Sensors are integrated flow and temperature measurement systems designed and validated for harsh aqueous environments. The system elements are a flow pipe with an integrated bluff body and a differential pressure sensor. The flow measurement is based on the Vortex principle. When a bluff body is placed in a flow inside a pipe, a series of vortices will be generated periodically on each side of the bluff body. These vortices propagate down steam giving rise to periodic pressure variations, which can be detected by the differential pressure sensor. The frequency of the pressure variations is proportional to the volume flow through the pipe. Operating principle The bluff body is designed to optimize to pulse strength of the pressure variations at the position of the differential pressure sensor. The bluff body is an integrated part of the injection molded flow tube, whereas the miniature differential pressure sensor is mounted through a slit in the tube, ie. flow ranges is set by the tube diameter, which is easy to modify. The differential pressure sensor key elements are a silicon bulk micro machined chip and a microprocessor-based signal-conditioning circuit, both on the same PCB. The conditioning circuit converts the pressure reading to a signal proportional to the volume flow through the pipe. The electronics are protected in an IP class 44 composite housing. In water the minimum detection of flow is 1.3 litre/minute in a 10mm pipe. For other pipe diameters please refer to the table on page of 17

11 The uniqueness of the chip is that the pressure and temperature sensitive area (the membrane region) is coated on both sides by an extremely corrosion and diffusion resistant thin film. The coating provides direct environmental robustness of the chip. This is the key technology making the high level of integration and miniaturization of the flow sensor possible. The chip has a square membrane, which deflects due to pressure. Strain gauges are incorporated in a Wheatstone bridge configuration on stress intensive positions on the membrane. The temperature coefficient of the bridge resistance is used as temperature sensor. The separation of the media and media-free zones is provided by an O-ring sealing. The sealing is centered around the membrane, and symmetrically on both sides of the chip, to ensure minimum stress coupling from the packaging. The sensor chip and the electronic components are mounted on a PCB using a combined chip on board and a lead free SMD technique. The exterior composite housing defines the pressure inlet sealing geometry. It is furthermore the carrier and environmental protection of the PCB. The media exposed part of the housing is one piece with one O-ring sealing to the atmosphere. Pressure port (one on pressure sensor, two on flow sensor) O-ring that seals water from electronics Sensor housing Guiding element for o-ring Electrical contacts to PCB Printed circuit board (PCB) Sensor chip (membrane detects pressure and temperature) Protective coating (resistant to corrosive media at high temperatures) Cross section of sensor chip and sealing configuration. 11 of 17

12 Signal Conditioning The non-compensated signals from the pressure and temperature detection circuits are feed into a microprocessor and converted to the digital regime after amplification. The microprocessor conducts algorithms to overcome pressure offset prior to and frequency detection of the pressure pulses. The frequency is converted to a flow based on calibration data, which are dependent on the geometry of the flow tube. The calibration data is programmed in the production line via a digital bus. The bus (optionally connected to the external pins) also communicates the calibrated sensor signals and provides control to system check procedures. On the pins the calibrated signals are reconverted to analog, ratiometric V signals. Sensor chip Micro Calibration & temp. comp. D/A 0,5-3,5V out P-cell Amplifier A/D Calibration data T-cell Amplifier A/D Frequency detection Frequency to flow conv. D/A 0,5-3,5V out System check Bus Digital out (prog, F & T out, test) Block diagram of the electrical functions 12 of 17

13 Exploded view of the sensor. 13 of 17

14 IV. Validation High reliability and safe robustness margins of the sensor is ensured by combining Grundfos experience in using composite materials in boilers, knowledge on sensor packaging, design for SIX SIGMA and an intensive and demanding test program. Selected results attached. Test Types Title Validated Functional (installation) Cable and Sensor connection (n=2-5) Minimum flow detection SW acceptancetests Pressure Drop < 400 mbar at max flow Line rejects < ppm (n=3000) Performance (validation) Linearity over temperatur span: C (n=20-30) Vibrationfree > 2G Responsetime temp < 3 sec Responsetime pressure/flow < 1 sec Reliability (call rate) Scaling/Lime: >> than typical competitor products (n=50-100) Condensation: IEC Magnetite: standard Grundfos test Sand >> than typical competitor products Thermic Stress: > 1000 cycles, -40 to 125 C Thermic Shock: > 4000 cycles, 10 to 95 C Pressure cycling: > /0-10 bar Acedic: 10 days/50 C/10% lemon acid Alcalic: ph11 90 C/3 months within FS Mechanical stability of housing > 500 hours at 90 C Storage and Transport: ISTA 1A 2001 Robustness (limitations) ESD: EN (n=2-5) HALT: T. and T. Shock, P and P shock, G shock Cavitation: Standard Grundfos test Corrosion test of sensor housing (PPS) Burst Pressure > 40 bar (30 min.) Burst Pressure > 15 bar (every 30 sec.in 4 weeks) Waterhammer: 27,5 bar/ cycles Safety (CE marking) IP44 enclosure: Standard Grundfos test (n=2-5) Drinking water approvals: WRAS, (ACS, DVGW, TZW) Emission: EN Emission Limit Class B Immunity: EN Field test (intended use) Continous remotely monitored boiler tests (various manufacturers) continously (n=10) on-going Full test plan and selected abstracts available upon request. 14 of 17

15 V. Options Lower/higher flow ranges incl. other flow measuring principles. Flow pipe supplied by Grundfos in composite (drawings on standards on request) PWM output signals (request) Frequency output signals (request) Digital Interface (bus communications available as RS232) Other Hydraulic Connections (different fittings exists as standards) 15 of 17

16 Attachment A: Pressure Drop Curves Pressure drop [mbar] Pressure drop as function of flow (sensor and flowpipe) VFS 1-20 VFS 2-40 VFS Flow [% F.S.] of 17

17 Attachment B: - Operation of flowsensor with various contents of glykole. Minimum flow Minimum Flow as function of glykole contents and media temperature 20 C 60 C % Glykole in water The accuracy of the flowsignal is unaffected by the viscosity of the fluid. However, the minimum flow that can be measured using the vortex flow principle changes with the viscosity and temperature of the fluid. As long as the amount of glykole is 30% or less, and the temperature of the liquid is 60 C or higher, the sensor is at a minimum flow of 3,3 litre/minute. At these conditions, the pressure drop over the sensor is 0.15 bar at 10 l/min. 17 of 17