Microprocessor driven digital flow controllers allow one to program, record, and analyze flow rates of various gases with a computer via an RS-485 interface (optional RS-232 is available).
Metered gases are divided into two laminar flow paths, one through the primary flow conduit, and the other through a capillary sensor tube. Both flow conduits are designed to ensure laminar flows and therefore the ratio of their flow rates is constant. Two precision temperature sensing windings on the sensor tube are heated, and when flow takes place, gas carries heat from the upstream to the downstream windings. The resultant temperature differential is proportional to the change in resistance of the sensor windings. A Wheatstone bridge design is used to monitor the temperature dependent resistance gradient on the sensor windings which is linearly proportional to the instantaneous rate of flow. The output of the Wheatstone bridge is converted to digital format with a 12 Bit ADC (analog to digital converter).
| Accuracy | 15°C to 25°C and 0.7 to 4 bars: ±1% of FS, 0°C to 50°C and 0.3 to 10 bars: ±2% of FS,±1% of FS at a specific temperature and pressure with special calibration |
| Repeatability | ±0.15% of full scale |
| Response Time | 0.6 to 1.0 s to within ±2% of set point over 20% to 100% of FS |
| Temperature Coeffcient | 0.05% of FS/°C |
| Pressure Coefficient | 0.01% of full scale/0.07 bar |
| Optimum Gas Pressure | 1.73 bars |
| Maximum Gas Pressure | 70 bars |
| Maximum Differencial Pressure | 3.4 bars for DFC2600 and DFC3600, 2.8 bars for DFC4600 |
| Gas/Ambient Temperature | 5°C to 50°C |
| Communication Interface | RS485 - Standard, RS232 - Optional |
| Output Signal | Linear 0-5 V= (2000 ohms min load impedance), 0-10V= (4000 ohms min impedance), 4-20 mA optional (0-500 ohms loop resistance) |
| Circuit Protection | Built-in polarity reversal protection. Resettable fuses provide power input protection. |
| Materials in Fluid Contact | 316/416 stainless steel, Viton/Neoprene/Kalrez O-rings (depends on model) |
| Attitude Sensitivity | No greater than +15 degree rotation from horizontal to vertical (standard calibration is in horizontal position) |
| Connections | Model DFC26 standard 1/4” compression fittings, Model DFC36 standard 1/4” compression fittings, Model DFC4600 standard 3/8” compression fittings, Optional 1/8” or 3/8” compression fittings and 1/4” VCR7 fittings available. |
| Leak Integrity | 1x 10-9 ml/s of helium |
| Transducer Input Power | +15V=, 450 mA maximum |
| Calibration Options | Standard 10 point NIST calibration (Optional up to 9 additional 10 point calibrations may be ordered for an additional charge) |
| CE Compliance | EN 55011 class 1, class B; EN50082-1 |
