Full-featured, fixed-installation liquid flowmeter

The DF868 is a full-featured, fixed-installation liquid flow meter designed to meet all your flow metering and energy measurement needs. Its patented Correlation Transit-Time digital signal processing provides drift-free measurements in ultraclean and most "dirty" liquids. This includes fluids with gas bubbles and entrained solids that previously required Doppler-type meters.

Dual-Channel Version Reduces Costs and Improves Performance

The optional dual-channel/dual-path model can be user-configured for a variety of applications. It can be set up to measure flow in two separate pipes with one meter to reduce the cost-per-measurement point. To minimize the effects of flow profile distortions, flow swirl and cross flow, and for maximum accuracy, you can install two sets of transducers on the same pipe.

Measure Flow from Outside the Pipe

Using clamp-on flow transducers, the DF868 measures flow rate through metal, plastic or even concrete-lined pipes without penetrating the pipe wall. To hold clamp-on transducers in place, a variety of clamping fixtures are available to accommodate different pipe sizes, transducer types and attachment methods (e.g., chain, wire rope, Velcro strap, magnetic, bolt-on or weldable steel yoke with metal band). Our universal clamping fixture includes ruled slide tracks to simplify transducer spacing for accurate flow measurements. There's even a special small-pipe clamping fixture with miniaturized transducers to simplify flow measurement on 0.5 to 2 inch lines.

Wetted Transducers for Maximum Accuracy

Obstructionless wetted transducers are readily available for maximum performance. After proper installation, transit-time accuracies of better than 1 percent are achievable in most applications, matching the performance of expensive factory-calibrated meters. Measurement range is 0.1 to 40 ft/s (0.03 to 12.2 m/s) for a turndown ratio of 400 to 1 in pipes from 1 to over 200 inches in diameter. Measurement is noncontaminating, obstructionless and causes no pressure drop. The DF868 is all digital so measurements don't drift, and it doesn't need regular maintenance since there are no moving parts to wear out or orifices to clog.

Dual-LCD Display, Datalogger and a Wide Variety of I/O Options

Whether single-channel or dual-channel, all DF868 meters feature two independent user-programmable graphic LCDs, giving you simultaneous access to more data. You have complete flexibility to display any parameter(s) on either LCD in a variety of numerical and graphic formats. Examples include numerical display of real-time flow measurements, real-time flow graphs and diagnostic waveforms, and numerical/graphic display of data from the meter's built-in 43,000-point datalogger. You can also add up to 12 isolated 4 to 20 mA outputs, up to six hermetically sealed or standard alarm relays, and up to 12 frequency/totalizer outputs.

Built-In Energy Measurement Capability

Another feature that makes the DF868 meter such a powerful and versatile flow meter is the energy measurement software included in every meter. The DF868, with optional RTDs and input boards, extends the benefits of ultrasonic flow measurement to energy measurement. Benefits include measurement of flow and temperature without pipe penetration and compatibility with pipes from 1 to 200 inches (25.4 mm to 5 m) in diameter. The DF868 meter measures energy flow in water and water/glycol heating and cooling systems with temperatures from -20 to 210°C (-4 to 410°F). Consult GE Infrastructure Sensing for use with other liquid systems.

To ensure compatibility with existing or preferred temperature instrumentation, the DF868 meter is available with three analog input boards. The transmitter input board provides 24-VDC loop power and two isolated 4- to 20- mA inputs for transmitters. For applications requiring raw RTDs, the RTD input board provides two isolated three-wire RTD inputs for temperatures from -100 to 350°C (-148 to 662°F).

Applications

The DF868 liquid flow meter is a complete ultrasonic flow metering system for measurement of:

The difference between the downstream and upstream transit times is proportional to the velocity of the flowing liquid, and its sign indicates the direction of flow.

The DF868 Flowmeter Uses the Transit-Time Flow Measurement Technique

The transit-time technique uses a pair of transducers, with each transducer sending and receiving coded ultrasonic signals through the fluid. When the fluid is flowing, signal transit time in the downstream direction is shorter than in the upstream direction. The difference between these transit times is proportional to the velocity of the flow. The DigitalFlow DF868 measures this time difference and uses programmed pipe parameters to determine flow rate and direction.

Automatically Adjusts to Changing Fluid Properties

Our unique Automatic Tracking Window™ (ATW™) feature, standard in all DigitalFlow DF868 meters, ensures accurate flow measurements even when fluid properties are unknown or changing. Like the seek mode on a car stereo, ATW dynamically sweeps the receiver window whenever the sound speed of the fluid changes. This powerful feature enables flow measurement when the fluid sound speed is unknown, when it is changing due to large temperature shifts, or when a new liquid starts to flow in a multiproduct pipeline.

ATW works for both clamp-on and wetted transducer applications by searching for a reliable ultrasonic receive signal. It does this by varying the time between the transmit signal and the receive signal window until the receive signal is found. The tracking window automatically sweeps through a range of time intervals based on the minimum and maximum expected sound speeds programmed by the user.

The window moves (tracks) in response to changes in the fluid sound speed. Once the optimal signal is found, ATW locks onto it until another large change in sound speed occurs.When this happens, ATW returns to the seek mode until the optimal signal is found again.

Is Built to Be Economical and Stay Economical

To be of real value, a flowmeter must be as economical to own and operate as it is capable in the field. Using the latest microcircuit and manufacturing technologies, the DigitalFlow DF868 flowmeter is built to stay in service for many years. Completely solid state, the DigitalFlow DF868 rarely wears out or needs servicing, resulting in little downtime and low maintenance costs.

The DigitalFlow DF868 will continue to save money by streamlining the measurement process and trimming labor costs.