Technical Specification of the Titan Metraflow
Non-Invasive PFA Ultrasonic Flow Meter
1/8” tube 20 to 1000 ml/min
1/4” tube 100 to 5000 ml/min
± 0.5% FSD (* ±1% reading)
PFA Tube; FDA Approved
±0.1% plus ±0.02% FSD
1/8” tube 27.7bar(g)@25°C; 20.8bar(g)@60°C
1/4” tube 16.7bar(g)@25°C; 12.6bar(g)@60°C
6 digit LCD configurable with annunciators
Configurable 2 X “NPN” NFET input or output
1 X “PNP” PFET input or output
4 to 20mA
0 to 5/10V dc
Interface and programming connection (Mini B)
Rate and/or Total
High/low flow alarms with hysteresis
Analogue outputs (4 – 20 mA, 0 – 5/10V)
Pulse output up to 10kHz
12 to 24V dc
USB 5V with limited functionality
Fluid 300mm tube tails
Electrical Via 8 way cable and/or USB
1/8” tube 240-020
1/4” tube 240-025
* ±1% Reading in isothermal conditions963748
Low flow measurement and temperature effects
There will always be a small amount of “background noise” due to ultrasound remaining within the tube between successive pings. This should be zeroed for best accuracy.
The noise affects low end performance and accuracy across the whole temperature range. The meter is calibrated at ambient temperature, typically 21 to 25°C. To zero the background noise fill the meter with fluid under pressure at the desired metering temperature. Stop the flow and press the two buttons on the top of the meter simultaneously for 5 seconds. The display will change to a flashing “——“ while the measurements are being taken. When the measurement is complete the display will change to “ZERO”. This cannot be done if liquid is flowing and the display will show “Flo” to indicate this. This zeroing will affect future calculations and the meter will give the best accuracy over the whole flow range for the temperature at which the system was zeroed. If the temperature of the tube changes, the position of the noise and its effect on the calculation will change. This is in the order of ±0.25 to 0.5% FSD if the system is not “zeroed” at the actual fluid running temperature. If measurements are required over a temperature range we would recommend stopping the flow and nulling the system at a mid-point in the desired temperature range. This will reduce the FSD error considerably.
After the unit is zeroed lower flows than specified can be registered but the accuracy is likely to be poor. To register these lower flows the “Cut off” in the “Calibrations settings box” should be set to just above 0.00 and at a flow rate above the point the meter records flow when none is happening but below the minimum flow specified for the meter. If it is set to 0.000 residual background noise will cause small readings even when there is no flow. If readings are seen increase the value sequentially until no output is recorded. Typically around 0.002 l/min.
The response time of the meter is not constant and is slower with lower flow rates. At full flow it is in the order of 50ms but at lower flows several seconds. This improves repeatability for the digital outputs and is similar in effect to the viewing filter when using the analogue outputs.
If the meter is subjected to heavy pulsations in the flow, for example from a diaphragm pump, it is recommended that a pressure regulator and a pulsation damper are installed upstream of the flowmeter. A length of flexible tubing with an in-line restrictor towards the end are often effective. The median filter should be set to 1 and it may be necessary to set the display filter to a high value. The Metraflow’s internal cycle time is not adjustable, is independent of the response time and should this measurement period coincide with, or be close to, the pulsations in the flow, very large errors in the flow calculations will occur.
Gas Entrainment or Modulating Fluids
Fluids which entrap gasses or seriously modulate the ultrasound will cause problems with the time of flight measurement. This might include viscous fluids being re-circulated from a small volume reservoir or Glycol type fluids.
Gasses seriously affect the ultrasound and should be avoided. It is recommended that the meter is always installed in a positive pressure system with a back pressure of at least 0.5 Bar plus 2 times the fluid vapour pressure. It is preferable to install the meter in a way that any trapped vapour can escape the flow measurement section. i.e. in a vertical line with the flow upwards.
The meters are calibrated on water at ambient temperature typically 21 to 25°C.