Compressed Air Flow Measurement Meter
In most industrial facilities Compressed Dry Air (CDA) is a primary component of overall energy use. In fact, compressed air is considered to be the “fourth utility” after electricity, natural gas and water, and its cost is very often higher than the other three when compared by cost per delivered unit of energy. An efficient compressed dry air system effectively balances six basic aspects — total demand, output air quality, operational supply, system storage, on demand distribution, and overall management. All six elements must work together for the system to reach its maximum efficiency. As the costs of energy continues to rise, accurately tracking the use of compressed air with Master-Touch™ flow meters can provide direct and immediate benefits by giving you the information you need to establish a program that:
Determining the true demand in a compressed air system, whether for a new installation or for an upgrade, can be a difficult task but it is critical first step in any design. Once operational, the demands upon a system will typically fluctuate significantly. In either case, the most accurate method of monitoring the system is through the use of one or more flow meters installed at strategic locations in the facility served by the system.
Potential points of measurement in a compressed air flow meter are:
For many years compressed air was most commonly measured by differential pressure orifice plate flow meters. Unfortunately, their very method of measurement — the plate pressure differential — creates a significant pressure drop in the system. Due to the square function characteristics of the pressure drop, the meters typically have a very limited turndown of approximately 5:1, making them unsuitable for monitoring system leaks or even off-peak usage. And if mass flow rate outputs are required, manual or computer calculations incorporating physical process measurements such as absolute pressure, differential pressure, temperature, and viscosity readings must be applied to the output signal to obtain the correct flow rate. Pressure drop, limited turndown and complexity are the necessary evils of using orifice plates to measure the flow rate of compressed air. The introduction of thermal mass flow meters addresses these inherent problems.
Thermal Technology for Compressed Air Flow MetersConstant temperature thermal mass flow meters, such as those produced by EPI, operate on the principle of thermal dispersion or heat loss from a heated Resistance Temperature Detector (RTD) to the flowing gas. Two active RTD sensors are operated in a balanced state. One acts as a temperature sensor reference; the other is the active heated sensor. Heat loss to the flowing fluid tends to unbalance the heated flow sensor and it is forced back into balance by the electronics. With this method of operating the constant temperature sensor, only the skin temperature is affected by the fluid flow heat loss. This allows the sensor core temperature to be maintained and produces a very fast response to fluid velocity and temperature changes. Additionally, because the power is applied as needed, the technology has a wide operating range of flow and temperature. The heated sensor maintains an index of overheat above the environmental temperature sensed by the unheated element. The effects of variations in density are virtually eliminated by molecular heat transfer and sensor temperature corrections. Therefore, thermal mass flow meters are now the preferred choice for use in compressed air systems.
Compressed Air Flow Meters: Specifying the RequirementsA number of factors must be considered when selecting and specifying any instrumentation and this is true for thermal mass flow meters to be used in compressed air systems. To specify the best configuration, you must determine:
What are the flow measurement conditions, such as the minimum and maximum flow rates* to be measured, the process pipe size, the air temperature and line pressure?
Where will the flow meter be installed and what is the piping configuration upstream and downstream of that location?
Is there moisture present at the point of measurement?
Master-Touch™ thermal flow meters provide real-time mass flow measurement and totalization for continuous CDA flow monitoring. A variety of sizes and configuration are available to meet virtually any installation requirement. One very common strategy is to use insertion style flow meters with ball valve assemblies that hold the flow meter firmly in place and yet allow the flow meter to be removed and reinstalled as necessary while preserving the air line’s integrity. If the survey of a compressed dry air system rotates from line to line throughout a large system, multiple ball valve assemblies can be installed at all points of measurement. Then, flow meters can be installed in the desired locations for the duration of the survey and moved on to new locations for the next series of measurements. In this way, a very large system can be monitored efficiently and economically.
for CDA Measurement —
Model 8840MPNH with
ball valve assembly