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Ultra Low Flow Meter Installation & Zero-Point Stability
Quick Answer: The mechanical mounting of the meter body controls zero-point stability more than the flow tube design when you measure below 2 kg/h. A meter bolted to a thin sheet metal bracket can drift 0.02 kg/h from a door slam. Bolt the same meter to a solid steel plate on a concrete pad and the drift stays under 0.003 kg/h for weeks. For ultra-low flow applications you should verify zero on site with the process fluid at operating temperature and pressure. Otherwise the flow total you report is mostly installation noise.
What Really Moves the Zero Point on a Micro Flow Meter
Small Coriolis tubes are stiff. The electronics pull a weak signal from a pair of sensor coils that measure tube twist. Any external stress that bends the meter case just a few microns changes the mechanical zero. This shift looks exactly like a small flow signal to the transmitter. Temperature gradients do the same thing faster. If one process flange is warm and the other is cold, the two sensor coils sit at different temperatures. The phase offset between them triggers a false mass flow reading. We have seen this on many customer sites: a chemical injection skid in Thailand read 0.08 kg/h of additive flow with the pump off. The root cause was a pipe clamp fixed to a wall that warmed up in the afternoon sun. After we moved the clamp one metre away from a direct sun path, the off-flow reading dropped to 0.003 kg/h.
Because small thermal mass makes the tube sensitive, most engineers skip this part. They trust the factory zero and hope for the best. In practice you need a field zero check anytime the meter is relocated, the gasket type is changed, or the process temperature shifts more than 20 °C from the last valid zero.
Mounting Rules That Keep Zero Drift Below 0.005 kg/h
Here is the thing: the pipe itself becomes the primary support for meters smaller than DN03. You cannot hang a 2 kg instrument from a thin 6 mm tube and expect a stable zero. Build a rigid L-bracket from 10 mm steel plate. Weld or anchor it directly to a concrete floor or a main structural beam. Do not attach the bracket to a vibrating pump base or a handrail. Separate the meter from any source of impulse vibration. A dosing pump pulsing once per second couples energy through the pipe wall into the sensor tubes. The meter electronics cannot filter out 1 Hz mechanical noise if the amplitude is high. Short flexible hoses before and after the meter help, but they are not a substitute for a solid base.
Pipe alignment matters much more than straight run. A DN02 meter body does not care about upstream elbows for flow profile. But a 1 mm lateral offset between the process pipe and the meter flange applies a bending moment that locks stress into the case. Use a dial gauge on the flange face if you can. Bolt the meter loosely first, check that all four bolts can turn by hand, then tighten in a cross pattern to half torque followed by full torque. This sequence matters. We had a food flavour producer in Mexico who swapped a gasket without loosening all bolts. The zero shifted from 0.002 kg/h to 0.017 kg/h and stayed there for two days until we loosened and re-tightened in the correct order.
Field Zero Procedure That Works the First Time
Flood the meter completely with liquid and wait until the temperature reading on the transmitter display is stable. Close both block valves with the meter full. The process liquid must be free of gas bubbles. For fluids above 50 cP viscosity, allow 10 extra minutes for thermal soak because high-viscosity fluids trap small heat pockets near the wall. Open the transmitter menu and start the zero calibration. Do not touch the meter or the pipe during the 30 to 60 seconds the routine runs. Vibration from a passing forklift or a closing valve 5 metres away can corrupt the result. Many Silver Instruments MFS2000 micro Coriolis models report a standard deviation after the zero run. Reject any result where the deviation is above 0.001 kg/h. Repeat the zero up to three times and take the median if you see variation linked to factory noise.
For services that switch between two different liquids, save a separate zero table. This is a feature available on the 4-20 mA HART and Modbus RTU versions of our meters. A solvent flush will leave a different stress pattern in the meter than a heavy fuel oil. A quick field zero after the product switch eliminates a 0.005 to 0.01 kg/h offset that would otherwise land in your batch report.
When Zero Stability Specs Do Not Tell the Full Story
You often see data sheets claim a zero stability of 0.01 kg/h. That number is valid only under laboratory conditions: ambient 22 °C plus or minus 1 °C, rigid heavy base, water at 0 bar back pressure, and no pipe stress. A real installation in a wastewater dosing container in Australia, where the morning temperature starts at 8 °C and climbs to 35 °C by noon, can deg
Electrical noise also masquerades as zero instability. Route the sensor cable away from VFD motor cables. Use a ferrite clamp on the cable shield at the transmitter end if the cable run exceeds 20 metres. A single unshielded 4-20 mA pair run parallel to a pump power cable can inject 50 Hz ripple that shows up as 0.002 kg/h noise floor on the flow output. Most engineers catch this only after they see the loop current wanders even with the block valves shut.
Specific Installation for Gas and Volatile Liquid Services
Ultra low flow gas measurement pushes the zero stability requirement even harder. A Coriolis meter measuring 0.1 kg/h of nitrogen at 10 bar has only a fraction of the signal amplitude of a liquid application. The mechanical mounting stiffness must be at least three times higher. Consider a secondary steel plate braced against the building column. The back pressure on the meter must be high enough to prevent expansion cooling that creates liquid mist or frost on the tube. Frost reduces the signal fast and can push the zero off by 0.5 kg/h. One of our customers running refrigerant dosing in a research facility in Saudi Arabia solved this by pre-loading the gas line with a small back pressure regulator set to 15 bar, keeping the meter in a single-phase zone at all times.
For liquid services that tend to form micro-bubbles, such as heated sugar syrup or polymer solutions, install a simple bubble trap pot just upstream. The meter will not ignore bubbles that pass through the tube, and the zero will shift during the transient. A small in-line sight glass after the trap gives you a quick visual check before you trust the batch total.
Quick Reference Table for Ultra Low Flow Installation Checks
Use this checklist before you power the transmitter.
Base support: 10 mm steel plate minimum, bolted to a structure heavier than 50 kg.
Pipe stress: zero force on flanges when bolts are loose.
Temperature gradient: difference across meter body below 5 °C at steady state.
Vibration: no visible movement of liquid surface in a nearby open tank.
Electrical noise: separate conduit for sensor cable, ferrite clamp fitted.
Cable gland: sealed and drip loop provided, moisture inside the junction box kills zero.
Frequently Asked Questions
How often should I re-zero an ultra low flow Coriolis meter?
Check the zero reading every month. Perform a field re-zero if the ambient temperature shifts more than 15 °C from the last valid zero, after any pipework change, or if the batch weights drift beyond 0.5 percent. A meter running 24/7 on stable process fluid may stay within spec for six months.
Can I use flexible hoses to avoid pipe stress on a DN01 meter?
Yes, short braided flexible hoses of 100 mm length can isolate pump vibration. But the meter body still needs a rigid support. Do not let the hoses carry the meter weight. Secure the meter to a bracket and let the hoses connect without pulling on the flanges.
The zero is stable but the flow reading oscillates at low cut-off. What should I check?
Trapped gas is the most common cause, even a single 0.5 mm bubble on the tube wall. Flush the meter at high flow for 30 seconds to sweep bubbles out. If the oscillation returns, check the inlet pressure and increase back pressure to raise the boiling margin.
Do I need to order a special mounting kit for a micro flow meter?
Silver Instruments supplies the meter with a standard mounting block for DN01 to DN03 sizes. For installations on vibrating platforms or in ATEX Zone 1 areas, request a reinforced bracket with damper pads. Send us your vibration frequency data if you have it.
What accuracy can I expect after a correct installation and field zero?
For flow from 0.2 kg/h to 10 kg/h you can expect a mass flow error below plus or minus 0.1 percent of rate plus a zero stability error around 0.003 kg/h for a well-installed Silver Instruments MFS2000 meter. This matches what we see regularly on customer sites in Vietnam, Indonesia, and Australia where the mounting rules are followed.
Send us your fluid type, viscosity in cP, flow minimum and maximum in kg/h, pipe size in DN, and operating temperature. Our application team will recommend a meter model and verify if your planned bracket design will hold the zero. Reach us through the request form on flow-meter.com.au or directly at the Silver Instruments sales channel for a fixed price quote.
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