『Hontzsch Flow Meter Manual: Calibrating Rugged Insertion Vane and Vortex Probes for Exhaust Stacks』Related information(flow rotameter|digital flow meter|balo meter|hydraulic flow meter|volumetric meter|positive displacement meter|pitot tube flow meter|displacement meter|cfm meter|variable area flow meter|inline flow meter|differential pressure flow meter|calibrated flow meter|velocity meter|paddle wheel flow meter|oval gear flow meter|anemometer hvac|multiphase flow meter|doppler flow meter|thorpe tube flowmeter|heat flow meter)
Calibrating Rugged Insertion Vane and Vortex Probes for Exhaust Stacks
Quick Answer: In situ calibration on the stack gives a more reliable result than bench calibration. You need a stable plant load, a valid reference flow signal, and the correct insertion depth. Silver Automation Instruments recommends a field verification every 12 months for normal exhaust service.
Why Stack Probes Drift Over Time
Rugged insertion vane and vortex probes work in a dirty environment. Dust, moisture, thermal cycling, and vibration change the sensor response over time. The Hontzsch Flow Meter Manual for calibrating rugged insertion vane and vortex probes for exhaust stacks shows that drift is rarely linear. A probe may read high at low velocity and low at high velocity.
Most engineers skip this part. They assume a new probe stays within the factory limits. In practice we have seen drift of 3 to 8 percent within one year. At a cement plant in the Philippines the stack velocity reading shifted by 11 percent after only six months.
Required Site Data for a Useful Calibration
Before you touch the probe, record these values. You need the stack or duct internal diameter in mm. You need the gas temperature in °C, static pressure in bar, and expected velocity range in m/s. For wet gas, record the moisture content. Also note the sensor insertion depth from the duct wall.
For most exhaust stacks, the insertion depth should be 0.12 to 0.13 of the internal diameter. This places the sensor near the average velocity point. Do not calibrate at the wall boundary layer. The velocity there is low and unstable.
Calibration Procedure for Insertion Vane Probes
First, compare the vane probe against a calibrated reference device. Use a hot wire anemometer, a Pitot tube, or a reference insertion probe with a valid certificate. The plant must hold a stable load for at least 15 minutes before you record data.
Record three velocity values at the same point. The reference average becomes your target. If the vane probe reads more than 3 percent away from the reference, adjust the span factor in the transmitter menu. For the Silver Instruments Model SI-VT10, the default span factor is 1.000. A reading 5 percent low needs a span factor of 1.050.
Verify again after the adjustment. Take three new readings. The repeatability should be within 0.5 percent. If the probe jumps more than 2 percent between readings, check the bearing, the sensor cable, and the connector for dust ingress.
Calibration Procedure for Vortex Probes
Vortex probes need a different check. The shedding frequency is linear with velocity, but dirt on the bluff body reduces signal quality. Clean the bluff body before a field calibration. Alcohol and a soft brush work well with dry dust. For oily stack deposits, use a mild solvent and dry compressed air.
Set the inner diameter in the transmitter to match the actual stack or duct ID. A wrong ID creates a large volumetric flow error. In a 1.5 m stack, a 50 mm ID error can change the flow reading by
Then compare the velocity output to a Pitot traverse. Take at least ten points across the stack. Average them. Do not compare a single point probe to a single point reference unless both sit at the same depth and the same flow angle.
Model Pairing for Stack Gas Service
Silver Instruments supplies insertion vortex flow meters for clean and mildly dusty exhaust gas. The Model SI-VT10 covers stack diameters from DN150 to DN2000. It outputs 4-20 mA HART and a pulse output. The standard sensor works from -20 °C to 250 °C. For higher temperature stacks up to 350 °C, ask for the SI-VT10-H version.
For wet flue gas with moisture above 10 percent by volume, an insertion thermal mass flow meter often works better. Send us the gas composition and the dew point. We will recommend the correct probe length and transmitter profile.
Common Mistakes During Stack Probe Calibration
One mistake is calibrating at a low load. Stack velocity below 3 m/s creates an unstable vortex signal. Do not calibrate below 5 m/s unless the probe manual gives a specific low flow correction.
Another mistake is ignoring gas temperature. A 20 °C change in stack gas changes the volumetric flow calibration. Use the actual process gas temperature, not an assumed value from the datasheet. This detail causes repeat visits on exhaust stacks in Southeast Asia and the Middle East.
How often should an insertion vane probe be calibrated on an exhaust stack?
Every 12 months for normal service. For high dust above 50 mg/m3 or continuous operation above 200 °C, verify every 6 months. A drift check with a reference Pitot can be done in one to two hours.
Can I use a Hontzsch flow meter manual procedure for a Silver Instruments vortex probe?
Yes if the probe type and signal output match. Both devices use velocity as the primary measurement. Check your transmitter menu for the span factor and the inner diameter setting. Do not copy a gas density value from one probe to another without checking the gas composition.
What is the minimum straight run for an exhaust stack insertion probe?
For a round stack, install the probe at least 8 to 10 diameters downstream from any bend or damper. For a rectangular duct, use 6 to 8 hydraulic diameters downstream. If you cannot meet this, use a multi point traverse as the reference.
What signal output should I order for a stack gas flow meter?
4-20 mA HART is the standard for plant control systems. Add a pulse output if you need totalized flow in cubic meters. For ATEX Zone 1 stack locations, specify the Ex d housing and the correct gas group.
How do I get a quote from Silver Automation Instruments?
Send us your pressure in bar, temperature in °C, pipe size in DN, and flow range. Also include the gas composition and the required probe insertion length. We reply with a model selection and a quotation within one working day. Contact Silver Automation Instruments at Tel: +86-25-68650347, Whatsapp: +86-25-52155837, WeChat: +86 15365082610.
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