VA 500 - Flow meter for compressed air and gases
RS 485 interface, Modbus RTU, 4...20 mA analogue output for m³/h, Pulse output for m³.
Details
Why measuring compressed air flow pays off
Compressed air flow monitoring shows how much air individual machines, departments or production lines use and how compressed air consumption is distributed over the day. Costs can then be allocated internally by consumption and used as a key figure in energy management to ISO 50001 or in an energy audit to EN 16247-1. The baseline after the end of a shift points to leaks and permanent consumers; measurements before and after a measure show what it achieved. Load profiles with peak and base load are also the data basis for sizing pipes, dryers and compressors. Because it measures from outside, the VC 600 makes this consumption measurement possible on existing pipes without any intervention in the pipe.
How clamp-on ultrasonic measurement works on compressed air and gases
The VC 600 is an ultrasonic flow meter working on the transit-time (time-of-flight) principle. Clamp-on means the sensor measures from outside the pipe – non-intrusively, often also called non-invasive. Two piezo transducers in the measuring unit send ultrasonic signals through the pipe wall, alternately with and against the flow. The transit-time difference gives the flow velocity; velocity and pipe cross-section give the volume flow. The difficulty with gases: they conduct sound far worse than water, so only a small part of the acoustic energy passes through the pipe wall into the gas. The measuring unit of the VC 600 is therefore tuned to the wall thickness of the pipe so that enough signal arrives even at low pressure; from 3 bar(g) the instrument measures reliably in metal pipes. Structure-borne noise travelling in the pipe wall is absorbed by the damping mat in the quick-release clamping system.
Fitting with half-shells and quick-release fasteners, without intervention in the pipe
The quick-release clamping system in stainless steel 1.4404 consists of two half-shells with an integrated damping mat. It is placed around the pipe at a paint-free spot and closed with the four quick-release fasteners, alternating sides; the fasteners pull the half-shells evenly onto the pipe so that the transducers couple in with full contact. The measuring unit is then fitted and secured with two M4 screws. No ultrasonic gel or coupling pads are required, the spacing between the transducers is fixed by the measuring unit, and nothing more than a screwdriver is needed. Mounting location and straight pipe runs are part of choosing the measuring point; the details are in the operating instructions.
Selecting the measuring unit and clamping system for pipes from 25 to 90 mm
The quick-release clamping system is chosen by the outer diameter of the pipe, in ten sizes from 25 to 90 mm (¾″ to 3″). The measuring unit comes in two versions, tuned to wall thicknesses of 1.5 to 2.2 mm and of 2.2 to 5.0 mm; both fit every size of clamping system. Anyone who wants to measure several pipe sizes therefore needs only additional clamping systems, not a second instrument. What counts is the outer diameter, not the nominal size: a DN 50 steel pipe measures 60.3 mm, a "50" aluminium pipe 50 mm, a stainless steel tube to EN 10357 53 mm. In the order code, only the clamping system therefore carries the pipe-size code.
Commissioning: calculating standard volume flow in the device
A setup wizard guides the user through entering inner diameter, wall thickness, pressure and temperature; pressure and temperature can be fixed values or come continuously from external sensors. Finally the wizard checks the signal quality and confirms it. The VC 600 converts to the selected reference conditions itself – ISO 1217 ex works – and totalises consumption as a compressed air meter; via Bluetooth the CS SensorApp shows live values and trends.
Retrofitting flow measurement while the plant is running
Typical measuring points for a retrofit without shutdown are the supply line after the dryer, branches to individual halls or cost centres, the feed line to a machine with conspicuous consumption and high-pressure lines after a booster; nitrogen consumption can be assigned to individual points of use in the same way. The line stays closed, and no new connection in contact with the medium is created. The readings go via the selected interface to a data logger such as the DS 500 or directly to the energy management system.
Frequently asked questions about clamp-on flow measurement with the VC 600
| Feature | VC 600 |
| Measuring principle | ultrasonic transit-time difference, clamp-on |
| Measuring range | 0.08–20 m/s (F1); 0.08–25 m/s (F2) |
| Accuracy | ±1.5 % of reading ±0.3 % of full scale |
| Pipe outer diameter | 25–90 mm (¾″–3″); larger nominal sizes on request |
| Wall thickness | 1.5–5.0 mm (measuring unit B1 1.5–2.2 mm, B2 2.2–5.0 mm) |
| Pipe materials | steel, stainless steel, aluminium |
| Line pressure | from 3 bar(g); upper limit set by the pipe, not by the sensor; suitability for high-pressure lines assessed from pipe and operating data |
| Gases | compressed air, nitrogen; others on request |
| Calibration | factory calibration with certificate; standard via gas constant (D1), true gas calibration for the selected gas (D2); recalibration by sending in the measuring unit |
| Temperature | line −30 … +80 °C, ambient −20 … +70 °C |
| Reference conditions | ISO 1217 (20 °C, 1,000 mbar, dry), DIN 1343 normal conditions for Nm³ (0 °C, 1,013.25 mbar), 15 °C/981 mbar, 15 °C/1,013.25 mbar (gas-industry base, ISO 13443) |
| Inputs | pressure 4–20 mA or Modbus RTU (PTS 500); temperature Pt100/Pt1000 or 4–20 mA |
| Outputs per version | I1: 4–20 mA + RS 485 Modbus RTU · I2: 4–20 mA + IO-Link · I3: Ethernet with PoE, Modbus TCP + 4–20 mA + RS 485 · I4: M-Bus + 4–20 mA + RS 485 Modbus RTU; Bluetooth for the CS SensorApp |
| Display, memory | touchscreen; totaliser; data logger 50 MB (about 2 years at 10 min) |
| Supply, protection, location | 18–36 VDC, 7 W; IP 65; indoor use, not for explosive atmospheres (Ex areas) |
Examples for compressed air at 7 bar(g) and 20 °C, standard volume to ISO 1217, full scale at 20 m/s. The complete table for every clamping system is in the data sheet.
| Inner diameter | Measuring range at 7 bar(g) |
| 21.7 mm | 0.85–213 m³/h |
| 41.9 mm | 3.18–794 m³/h |
| 50.0 mm | 4.52–1,130 m³/h |
| 60.3 mm | 6.58–1,644 m³/h |
| 80.9 mm | 11.84–2,960 m³/h |
A thermal sensor protrudes into the pipe and therefore requires a ball valve or a measuring section; the VC 600 is mounted on the outside of the pipe. It measures the flow velocity across the pipe cross-section and converts this to standard volume using pressure and temperature; a thermal sensor measures the mass flow directly and must therefore know the type of gas.
Most clamp-on flow meters are designed for liquids. Gases conduct sound much less effectively, so a sensor unit is required that can transmit a strong enough signal through the pipe wall. The VC 600 has been developed for this purpose and measures flow in metal pipes from 3 bar(g) upwards.
The minimum pressure is 3 bar(g). The upper limit is not determined by the sensor but by the pipework, as the device is mounted externally and is not subjected to pressure. As the measuring range is specified in terms of actual flow velocity, the VC 600 measures high standardized volume flows at high pressures: At 40 bar(g) and an inner diameter of 50 mm, 20 m/s corresponds to approximately 5,800 m³/h, based on 20 °C and 1 bar absolute, using the ideal gas approximation.
In compressed air networks, a relative pressure sensor such as the PTS 500 or CS 16 is sufficient: The VC 600 converts a fixed air pressure value of 1,000 or 1,013.25 mbar to the absolute pressure required for the standard volume calculation. A change in air pressure of 30 mbar alters the standard volume at 7 bar(g) by only about 0.4 per cent. An absolute pressure sensor can also be connected and adjusted on the device.
This is because the pipe wall determines how much sound reaches the gas. The sensor unit is calibrated for a specific wall thickness range to ensure that a sufficient signal is received even at low pressure. One version covers 1.5 to 2.2 mm, the other 2.2 to 5.0 mm. Both fit all quick-clamping systems.
Part of the ultrasound signal travels further into the pipe wall and is reflected back at flanges, welds and bolted joints. The damping mat in the quick clamp system absorbs this structure-borne noise at the sensor unit. If a flange is situated close to the point of measurement or if the pipe is very rough, this can affect the signal. In such cases, damping clamps fitted upstream and downstream of the sensor – suited to the pipe size and no more than 50 mm from the quick clamp system – can help.
For steel, stainless steel and aluminium pipes with an outside diameter of 25 to 90 mm and a wall thickness of 1.5 to 5.0 mm. Aluminium pipe systems for compressed air with outside diameters of 25 to 80 mm fall within this range. The installation site should be free of paint, rust and weld seams.
±1.5 per cent of the measured value ±0.3 per cent of the upper range value, i.e. the same value as for the VA 550 and VA 570 thermal sensors in their standard versions. This is subject to the pipe data being entered correctly and the point of measurement complying with the installation conditions.
It displays this as the base load: any current remaining at the end of a shift is attributable to leaks and continuous consumers. Where residual quantities are very small, we will agree the measuring range and measurement uncertainty with you. The individual leak can then be located using the LD 500 leak detector or the LeakCam 600 acoustic camera.
Every VC 600 is calibrated on the CS INSTRUMENTS volume flow test bench prior to dispatch and is supplied with a calibration certificate. For recalibration, only the sensor unit needs to be sent in; the quick clamp system remains attached to the pipe.
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