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0.5 Kg/H Flow Meter High-Accuracy Dosing Procedures
Quick Answer: A 0.5 kg/h flow meter for dosing uses a Coriolis mass flow meter in most cases. It gives direct mass measurement at ±0.2 % of rate or better. The dosing procedure depends on a fast control valve, a small pipe size like DN4 or DN6, and a batch controller with millisecond relay outputs.
We see this low flow range often in catalyst injection, methanol dosing in oil and gas, or aroma addition in food factories. The challenge is not just the small flow rate. It is about getting repeatable shot weights when the target is 5 grams or 10 grams per dose.
Why 0.5 kg/h Needs a Coriolis Meter
A thermal mass flow meter can read 0.5 kg/h of gas easily. But for liquid dosing at this range, a Coriolis meter is the workhorse. Silver Instruments supplies a micro Coriolis flow meter series with tube bore as small as 0.8 mm. The measuring tube oscillates and detects mass flow directly. No moving parts. No drift from temperature changes if the meter has good density compensation. The output on the transmitter is 4-20 mA HART plus a pulse output for batch control. Most engineers set the pulse to 0.1 gram per pulse for fine resolution.
In a biodiesel plant in Malaysia, we helped a customer dose sodium methylate at 0.5 kg/h into a continuous reactor. The pipe size was DN6. Back pressure stayed at 2.5 bar. The meter tube was 316L stainless steel with PTFE lining on the electronics housing. They used an ATEX Zone 1 housing because methanol vapors were present. The dosing accuracy target was ±0.5 gram per shot, and the Coriolis meter delivered ±0.3 gram after tuning.
Pipe Size, Pressure, and Back Pressure Rules
Small pipes matter. A 0.5 kg/h flow of a light hydrocarbon means a velocity below 0.01 m/s in a DN15 pipe. That is too low for good control. We recommend DN4 or DN6 for this range. The pressure drop across the meter at 0.5 kg/h is almost zero—less than 0.1 bar. So the main pressure loss comes from the dosing valve and the nozzle. Keep a constant upstream pressure. We use a small nitrogen blanket on the tank at 1 to 2 bar(g) if the fluid is sensitive to air. Or we install a back-pressure regulator downstream to prevent flashing. In a paint dosing job in Vietnam, the solvent had a vapour pressure of 0.8 bar at 30 °C. They used a spring-loaded back-pressure valve set to 1.2 bar right after the meter. This kept the liquid in single phase.
Dosing Procedure Step by Step
Step 1: Pre-fill the line. Keep the meter tube full at all times. A tiny bubble in a micro Coriolis tube causes a measurement error of 2 to 5 %. Use a manual bleed valve at the highest point. Some setups use an automated vent cycle before every batch.
Step 2: Set the batch setpoint. On the batch controller, enter 500 grams or whatever the recipe needs. The controller from Silver Instruments accepts a start signal from a PLC via a dry contact. Then it opens a NC solenoid valve with a 24 VDC coil.
Step 3: Two-speed valve control. For 0.5 kg/h, the main valve stays open. But a second valve in parallel gives a trickle flow at the end. The rough dose opens a full port valve until 90 % of the setpoint is reached. Then the fine dose uses a small needle valve in parallel, adjusted to about 0.2 kg/h. This cuts off overshoot. In a customer site in Chile for mining reagent, they got ±0.2 gram repeatability with this method.
Step 4: Off-delay and line clearing. After the valve closes, a short air purge or a pinch valve squeezes the line to push the last drop. The batch controller logs the actual mass delivered. Data goes via Modbus RTU to the main PLC. We have seen a water treatment site in Saudi Arabia that sends the batch report directly to a paperless recorder for audit trail.
Key Parameters the Engineer Must Set
For a micro Coriolis meter on 0.5 kg/h duty, go into the transmitter menu and set these
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- Flow unit: kg/h
- Low flow cut-off: 0.005 kg/h or lower. Factory default is often 0.02 kg/h. That can mask real flow at the end of a dose.
- Damping: 0.2 to 0.5 second. Too high damping delays the batch stop signal.
- Pulse width: 0.5 ms if the PLC can read it. For a slow PLC, use 5 ms but accept a slight loss of resolution.
- Density calibration: perform a water calibration at 20 °C. A shift of 0.001 g/cm³ changes the mass reading noticeably on a micro tube.
Real-World Accuracy Numbers
On paper, a Coriolis meter has a rated accuracy of ±0.1 to ±0.2 % of rate. At 0.5 kg/h that is ±1 gram per hour. But batch dosing accuracy is not the same as steady flow accuracy. In practical tests with olive oil at 22 °C, we saw a batch deviation of ±0.15 gram for a 100 gram dose with a 2-second valve delay. When the delay was 0.5 seconds, deviation dropped to ±0.05 gram. The key is the valve response, not just the meter.
Mounting and Vibration Tips
Mount the meter on a solid bracket. Do not hang it on the pipe itself. A micro Coriolis tube picks up pump vibration easily. Use flexible hoses at the inlet and outlet. Keep the meter away from solenoid valve coils that create magnetic interference. In a food flavour dosing skid we built for a customer in Thailand, we used a stainless steel panel with rubber grommets to isolate vibration from the gear pump.
When an Oval Gear Meter May Work Instead
If the fluid is viscous and clean, a micro oval gear meter from Silver Instruments can also meter 0.5 kg/h. The smallest model has a 0.2 mL/rev displacement. But you must convert volume to mass with a density table. The dosing controller does that math if you enter the density value. The oval gear meter has a pressure drop of about 0.3 bar at 0.5 kg/h for a fluid of 10 cP. This is fine for many oils. However for volatile fluids, stick with Coriolis.
Silver Instruments Model Recommendations
For 0.5 kg/h liquid dosing, ask for the Silver Instruments micro Coriolis series with DN4 connections and NPT 1/4 inch threads. Request the IP67 transmitter with integral display. Specify the ATEX rating if needed. If your fluid is corrosive, we can upgrade the wetted parts to Hastelloy C-22. For gas at 0.5 kg/h, use our thermal mass flow meter with a laminar flow element. Tell us the medium, operating pressure in bar(g), temperature in °C, and pipe size DN. Send that info to our technical team and we will reply with a proposal and wiring diagram within one working day.
FAQ
Q: Can a 0.5 kg/h flow meter handle both liquid and gas?
A: No single meter does both well at this range. Use a micro Coriolis for liquid and a thermal mass meter for gas. The Coriolis works for gas too, but at 0.5 kg/h gas the pressure drop may be too low to maintain accuracy.
Q: What is the minimum batch size with a 0.5 kg/h meter?
A: We have seen reliable batches down to 2 gram. Below that, valve delay and pipe elasticity dominate the error. Use a positive displacement micropump with a servo drive for sub-gram shots.
Q: How do I prevent air bubbles in the meter tube?
A: Keep the pipe fully flooded. Install a sight glass upstream. Use a small back-pressure valve after the meter. In a batch start sequence, run the pump for 5 seconds to flush any bubbles before opening the dose valve.
Q: Does the meter need re-zeroing often?
A: For a fixed installation, perform a zero check once a month. Block the downstream valve, fill with process fluid, and run the zero function on the transmitter. Temperature swings more than 10 °C can shift zero slightly.
Q: Can I use a magmeter for 0.5 kg/h of conductive liquid?
A: A DN4 magmeter exists, but the minimum flow for a stable signal is around 2 L/h for most models. For a 0.5 kg/h water-like liquid, that is 0.5 L/h. The signal-to-noise ratio is too low. Stick with Coriolis or oval gear.
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