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Calorimetric Flow Meter: Thermal Inline Liquid Process Sensors
Quick Answer
A calorimetric flow meter for liquids uses a thermal measurement principle to deliver direct mass flow with no moving parts. It works on the basis of heat transfer between two PT100 sensors and the flowing medium. These inline sensors are a practical choice for small line sizes, low flow velocities, and applications where the liquid has a known, stable heat capacity.
How the Measuring Principle Works in Practice
The sensor body contains two temperature probes. One probe is heated constantly, the other measures the actual fluid temperature. As liquid moves past the heated probe, it carries heat away. The temperature difference between the two probes changes with flow rate. More flow means a larger cooling effect and a smaller temperature delta. The electronics inside the transmitter convert this delta into a mass flow reading in kg/h or l/min. Because the measurement relies on thermal conductivity and heat capacity of the liquid, the medium must be homogeneous and free of gas bubbles or solids. In practice, design engineers choose this technology for clean water, chemicals, oils, and solvents in lines from DN3 up to DN100.
Where Calorimetric Flow Meters Fit Best
Most engineers skip this part and go straight to Coriolis meters for mass flow. Here is the thing. Calorimetric inline sensors fill the gap where Coriolis is oversized or over budget. We have seen this on customer sites many times. A cooling water loop in a plastics plant in Vietnam only needed to verify that flow was present and above a minimum of 0.02 m/s. A DN15 thermal mass flow meter with 4-20 mA HART cost less than a third of a small Coriolis. The response time was under 2 seconds, fast enough for pump protection. Another example is chemical dosing in a water treatment plant in the Philippines. They inject a diluted polymer solution at 0.5 to 5 litres per hour. A calorimetric flow sensor with PTFE lining and 316L wetted parts gave a repeatability of ±0.5 percent of full scale. The plant technician set up a low-flow alarm directly via the relay output, no PLC programming needed.
Key Specifications You Will See in a Data Sheet
When you compare models, look for these items. The wetted material is typically 316L stainless steel, but Hastelloy and PTFE linings are available for aggressive chemicals. Process connections are usually G thread, NPT, or tri-clamp for hygienic use. The standard signal output is 4-20 mA plus HART. RS485 with Modbus RTU is a common option. Power can be 24 VDC loop-powered or 90-260 VAC with a separate transmitter. Accuracy is in the range of ±1 to ±2 percent of full scale, with a turndown ratio up to 100:1. Temperature ratings go from -20 to 80 °C for integral electronics and up to 180 °C with remote versions. For hazardous areas, SIL instruments supply ATEX Zone 1 and Zone 2 certified models. Inline wet-calibration on water is performed at the factory, and every sensor ships with a 5-point calibration certificate traceable to national standards.
Installation Tips That Prevent Field Headaches
Thermal mass flow meters for liquids need a fully developed flow profile. We recommend 10D upstream and 5D downstream straight pipe. In tight spaces, you can reduce this to 5D and 3D if you accept a small offset in the reading that can be corrected in the transmitter. The pipe must be completely full at all times. Air pockets on
Comparing with Other Flow Technologies
Electromagnetic flow meters need a minimum conductivity of 5 µS/cm. Calorimetric sensors have no such limit, so they can measure deionized water and non-conductive solvents. Ultrasonic clamp-on meters work on larger pipes but struggle with low flow below 0.1 m/s. The inline thermal probe handles velocities down to 0.01 m/s. Vortex meters create a pressure drop and need a minimum Reynolds number. The calorimetric sensor is obstruction-free, with a straight probe tip that adds almost no pressure loss. A paint manufacturer in Southeast Asia replaced a turbine meter on a resin line. The turbine bearings wore out every six months because of the sticky medium. A PTFE-coated calorimetric sensor with no moving parts ran for two years without maintenance. They now order this same model for all their solvent and hardener lines.
How to Get the Right Quote
Send us your process data and we will return a fixed price within one working day. We need: liquid name and concentration, minimum and maximum flow rate (in kg/h or l/min), operating pressure (bar), operating temperature (°C), pipe size (DN), and any hazardous area requirement. Email us at [email protected], call +86-25-68650347, or message on WhatsApp +86-25-52155837. Our WeChat is +86 15365082610. Silver Automation Instruments stocks common DN15 and DN25 models and can ship from our Nanjing factory to Sydney, Singapore, Dubai, or Johannesburg by air freight in under a week.
Frequently Asked Questions
Can the calorimetric flow meter handle deionized or ultrapure water? Yes. The measurement is thermal, not conductivity-based. Deionized water has a well-defined specific heat capacity and works well. This is a frequent win over electromagnetic meters that need a minimum 5 µS/cm.
What is the minimum flow velocity it can detect? Typical models can detect from 0.01 m/s in water. For very low cut-off settings, a special low-flow calibration is done in our lab. This is useful for leak detection or pump dry-run protection.
Does the sensor require temperature and pressure compensation? The transmitter already includes a reference PT100 for fluid temperature compensation. Pressure has a small effect on heat capacity in gases but in liquids it can be ignored for most industrial measurements.
Can I use one model for multiple liquids? The meter is calibrated for one specific fluid. If you switch from water to acetone, the thermal properties change completely and the reading will be wrong. You can store multiple calibration curves in the electronics if you order a multi-range unit, but you must tell us all fluid names in advance.
What approvals does Silver Instruments offer for hazardous areas? We supply ATEX Zone 1 and Zone 2 certified sensors with flameproof or intrinsic safety protection. IECEx certificates are available for countries that accept the IECEx scheme, which covers most regions in Asia, Africa, and the Middle East.