Ultrasonic flowmeter appeals to new markets
A new high-accuracy, low-cost ultrasonic flowmeter could represent a breakthrough in small bore flow metering.
Due to be launched at Mtec 2010, the Atrato from Titan Enterprise is a direct through meter without a contorted flow path. The device uses ultrasonic technology and can handle flows from laminar to turbulent. Because of this, it is said to be largely immune from the effects of viscosity. The supplier claims excellent turndown, linearity and repeatability for the part.
The Atrato is capable of monitoring flow over a range of 200:1 and has accuracy better than ±1.5%. Its simple design is said to make it marketable, while a USB interface makes it easy to install and use.
This device uses the favoured 'time of flight' measurement system, in which a signal is passed along the pipe with the flow and back up the pipe against the flow. With no flow, the signals are identical; when there is flow, thetime difference between these signals is proportional to the velocity of the liquid. As the pipe geometry is fixed and known, the throughput of the liquid can be calculated.
Titan's founder Trevor Forster has championed the technology for some time. "Fundamentally, my position is that the future of flow measurement is going to be ultrasonic or Coriolis based. They're the only two long-term viable technologies because they're non-intrusive."
However, until now, both technologies have been seen as expensive and – in the case of small-bore ultrasonic flowmeters – not particularly accurate. For these reasons, small bore ultrasonic flowmeters have tended to be restricted to medical applications. However, the Atrato's ability to achieve timing accuracies equivalent to 200picoseconds at between 25 and 50% the cost of other ultrasonic options could change this.
At the heart of the Atrato is its use of a different sensor arrangement and advanced signal processing to interrogate the flow, ensuring that that it provides high accuracy over a wide turndown range. Although preferring to maintain the signal processing as a 'black art', Forster is happy to discuss the patented sensor arrangement. "We're using an annular crystal. What we're looking to do is to excite the crystal across the radius. Normally, when you excite a crystal, you get a natural frequency and the movement goes across the width. We're exciting it in such a way that we're getting the movement radially, which puts a very, very strong signal directly into the fluid. The method of driving and receiving we use ensures that the resulting signals are identical and, at zero flow, the upstream and downstream signals cancel each other out."
This process offers the technology a number of advantages. Says Forster: "Because we are introducing the signal radially and receiving it radially, we've effectively got a plane wave travelling down the pipe, so we don't have contorted parts or reflected signals. This also gives us a signal to noise ratio of up to 3000:1, which is why we can handle such a wide flow range."
Because the signals are travelling in a plane wave, they are insensitive to the velocity profile. Indeed, running the meter on a 380 centistoke oil gives almost identical performance to running it on water. Naturally, this makes it adaptable across a number of markets. Applications which Forster believes will be of particular interest include pilot plant, research laboratories, medical and low industrial flows. However, Forster sees another potential market in domestic water meters. "We are looking for partners for the domestic water meter market. We're well within the flow range and performance level for domestic water meter. We're out on cost, but then we're not building 20 million a year, which is the anticipated market in a few years time!"
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