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Coriolis Mass Flow Controller Precision Tuning
Quick Answer: A Coriolis mass flow controller leaves the factory with a general purpose tune. That tune works for water at 20 °C and low viscosity. Most process fluids are not water. You need to adjust PID constants, drive gain, density offset, and filter settings for your actual fluid. Send us your process pressure (bar), temperature (°C), pipe size (DN), and fluid type. We will return a tuning file for your Silver Instruments controller.
Why a Factory Tune Causes Problems on Real Process Lines
The standard tune assumes a viscosity below 10 cP and a clean, bubble-free liquid. Many customers in Southeast Asia and the Middle East transfer chemicals, edible oils, or syrups. These fluids reach 100 cP or more. The drive circuit must work harder to keep the tube oscillating. With a low gain setting, the oscillation amplitude drops and the meter reports a low flow or a zero drift. One chemical blender in Malaysia saw a 6 percent under-reading on a 500 kg/h caustic soda line because the factory gain value was set for water. After we raised the drive gain and slowed the PID integral time, the error dropped below 0.5 percent.
Which Parameters You Can Adjust in a Silver Instruments Controller
Our Coriolis transmitters expose several tuning values via the local display, HART, or Modbus RTU. These are not hidden service menus. The most important are drive gain, filter time constant, PID Kp and Ki, and density offset.
Drive gain. Factory default is often 30 to 40 on a 0-100 scale. For viscous fluids, 55 to 70 stabilizes the tube. Too high a gain causes overshoot and noise. We have seen customers set gain to 95. The tube vibration then couples with pump pulses and the mass totalizer counts 15 percent high.
Filter time constant. A value of 0.2 seconds is common for water. For pulsing diaphragm pumps, 0.8 to 2.0 seconds removes noise without masking real process changes.
PID Kp and Ki. The factory PID values respond well to a step change in water. When you fill a batch tank with a high-viscosity fluid, the control valve reacts slowly. Lowering Kp by 30 percent and increasing Ki keeps the process variable from hunting.
Density offset. The meter calculates mass flow partly from the measured density. If you do not zero the density reading on your fluid, a 2 kg/m³ error at 2000 kg/h becomes a 1.2 kg/h mass error after one hour. A paint manufacturer in Vietnam cut batch mass deviation from 17 kg to 3 kg simply by entering the real density from a lab hydrometer.
On-Site Tuning Steps That Work Every Time
Here is the sequence our service engineers follow when commissioning a Coriolis flow controller on a new fluid.
Step one. Fill the meter tube with your process fluid and wait until the temperature stabilizes. The PT100 in the sensor reads true fluid temperature, not ambient air. Wait until the temperature varies less than 0.5 °C per minute.
Step two. Perform a zero calibration with the block valve closed. Never skip this step. A closed valve ensures no flow. Even a tiny leak across a seat will bias the zero by 0.2 to 0.5 kg/h. A zero drift that looks small adds up over a 48-hour batch.
Step three. Enter the known fluid density at operating temperature. If you do not have a density value, we can estimate it from
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Step four. Start flow at 10 percent of the full scale and adjust Kp while watching the control deviation. Move to 75 percent and fine-tune Ki. This two-point method catches the nonlinear behavior most viscous fluids show.
Common mistake: tuning only at low flow. A biodiesel plant in Indonesia tuned Kp at 200 kg/h on a 2000 kg/h full-scale controller. At 1500 kg/h, the valve oscillated violently. The team had to stop the batch and re-tune at high flow with a smaller Ki value.
When You Need an External Density Reference
For single-component fluids like methanol or toluene, the internal density calculation is accurate enough after a single field offset. Multi-component mixes change density with batch age, temperature, or absorption of moisture. An amine scrubber in a Nigerian gas plant saw its lean amine density drift from 1015 to 1030 kg/m³ over a weekend. The Coriolis controller mass total diverged by 0.8 percent per eight-hour shift. We recommended they take a sample to a lab hydrometer every 12 hours and update the density offset via Modbus. That simple routine brought custody transfer unbalance down to 0.1 percent.
Send Us Your Process Data for a Custom Tuning File
Do not experiment with PID tuning on a running process if you are not sure. Tell us what you are moving. We need fluid name or composition, operating pressure in bar, temperature in °C, pipe size (DN15 to DN80), and the required flow range in kg/h or l/h. Email these details to [email protected]. We can also log into your HART loop remotely and watch the tube frequency during a tuning session. Our team has done this for a 4000 kg/h thermal oil loop in Saudi Arabia and a 200 kg/h chocolate transfer in Australia. Both now run with less than 0.2 percent control deviation.
FAQ
Can I use the same tuning file for different fluids? No. Viscosity, density, and temperature response change from fluid to fluid. A tune set for 50 cP glycerol will not control a 5 cP solvent. Always load a fluid-specific file.
How often should I retune my Coriolis controller? We advise a zero check each time you change batches or every 300 operating hours. Re-tune the PID gains only when you see control oscillations or more than 1 percent mass balance error.
Will the factory tune work for diesel? Diesel at 20 °C has a viscosity around 4 cP. The factory tune usually works for diesel at low flow rates. At flows above 1000 kg/h, you may need to increase the filter time constant to reduce pump-induced noise.
What happens if I set the drive gain too high? The tube vibration becomes unstable. You will see random flow spikes of 5 to 10 percent. The totalizer can overcount seriously. We helped an edible oil customer who had gain set at 92. Their monthly mass balance error was 22 tonnes on a 5000-tonne throughput. Dropping gain to 68 fixed it.
Does Silver Instruments provide remote tuning support? Yes. We can connect to your HART or Modbus loop via a secure gateway and adjust parameters while you watch the process. We have done this for plants in Thailand, Egypt, and Chile. Send us your loop schematic and a Webex invite.
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