
IM-P505-02-US
Issue 1
8
UTM20 Series Ultrasonic Transit-time Flowmeters
4. Introduction
WARNING
This equipment includes some external non-metallic parts. The user shall therefore ensure
that the equipment is not installed in a location where it may be subjected to external
conditions (such as high-pressure steam) which might cause a build-up of electrostatic
charges on non-conducting surfaces. Additionally, cleaning of the equipment should be
done only with a damp cloth.
The UTM20 transit time meter measures volumetric flow and heating/cooling energy rates in clean
liquids as well as those with small amounts of suspended solids or aeration, such as surface water
or sewage. UTM20 ultrasonic flow and energy meters clamp onto the outside of pipes and do not
contact the internal liquid.
The UTM20 meter is available in two versions:
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A flow meter for water delivery, sewage, cooling water, alcohols, chemical
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A heating/cooling energy flow meter used in conjunction with dual clamp-on RTDs for temperature
measurement—ideal for hydronic process and HVAC applications
Transit time flow meters measure the time difference between the travel time of an ultrasound wave
going with the fluid flow and against the fluid flow. The time difference is used to calculate the velocity of
the fluid traveling in a closed-pipe system. The transducers used in transit time measurements operate
alternately as transmitters and receivers. Transit time measurements are bi-directional and are most
effective for fluids that have low concentrations of suspended solids and are sonically conductive.
Fig. 1 Meter operation
An ultrasonic meter equipped with heat flow capabilities measures the rate and quantity of heat
delivered or removed from devices such as heat exchangers. By measuring the volumetric flow rate
of the heat exchanger liquid, the temperature at the inlet pipe and the temperature at the outlet pipe,
the energy usage can be calculated.
By applying a scaling factor, this heat flow measurement can be expressed in various units (Btu,
Watts, Joules, Kilowatts and others).