Once you have assessed your industry and realized oy need a thermal flow switch, the next step is to select the best water flow switch to suit your needs. There are several characteristics of thermal switches that you should focus on.
We need to understand how a thermal flow switch works. First, as the name suggests, it works by detecting the heat as the fluid passes through a point. You will compare the heat of the fluid at a different location. But how does that work? Check the example below.
Know more: Why Is Dew Point Important for Flow Sensors?
When you are in a chilly environment, your body’s surface will lose the heat to the environment. However, there’s a point where the skin and the air temperature will balance. Thus, you will not feel too cold.
But when the air is in motion, your body will need to lose temperature constantly. Thus you will feel colder than in the first incident. A thermal flow switch works under the same principle.
You will find water flow switches with two nodes at point A and point B. A known voltage will heat the node at point A. Since the fluid will have a known temperature, the flow rate will be determined at point B.
At point B, the node will require a fraction of voltage to equalize the fluid temperature as it is at point A. Then you will calculate the difference between heat requirements at point B to equalize point A.
Another type of flow switch measures the temperature difference of fluid between point A and point B.
Below are the things you should look out for when searching for the water flow switches.
Flow Velocity Profile
Different fluids have different flow velocity profiles. The surface that touches the pipes to the channel is usually slower due to friction. The velocity increases as you move towards the center of the flow channel.
Thus, the flow velocity profile will determine the type of water flow switch that you choose. Ensure that the switch will gauge and act on the flow profile with ease.
When you understand the velocity profile, you can determine the velocity throughout the pattern. The accuracy of the switch will drop when the flow profile degrades. The piping and straight run upstream of the flow switch affects the accuracy of the system. The downstream run has a small impact on accuracy.
However, it is hard to acquire a perfect straight run in real life. The flow will get disturbance from valves, couplings, expanders, reducers, flanges, etc. Thus, it would help if you strived to have sufficient straight run before the switch to increase the accuracy.
People usually overlook the installation location of a flow switch. Yet, it is vital due to ease of installation and use. But why would you consider the location when you are selecting a flow switch? It is because the location of the switch will determine the location of flow disturbance.
Thus, you have to know the location in hand before you select your water flow switch. Every flow switch has a factory calibration. The manufacturer or seller can advise you on the best flow switch based on the expected flow disturbance.
Flow Meter Factory Calibration
For a thermal flow meter to function effectively, you need to install the probe within the flow channel. Thus, a manufacturer needs to understand the flow conditions of different fluids.
Thus, he will have several switches that will meet different fluids. Also, the calibrations of the switches should help in varied flow conditions.
When you go to buy a flow switch, have a list of your fluid parameters. It helps the seller to calibrate the switch to suit your fluids. Thus, you will have an easy time calibrating the switch to the accurate fluid conditions once you install it. During manufacturing, the following factors are looked at;
When the manufacturer makes a water flow switch, then they should use water as the testing fluid. It should be similar when they are making flow switches for other fluids.
It helps them to make the best flow switch for a particular fluid. The nest flow switch should be adjustable. Thus, you can calibrate it to your fluid requirements.
There are different size flow switches to suit different pipe sizes. If your firm is new and you are buying the first flow switch, you should do so after buying the pipes. Alternatively, you can buy it alongside the pipes. Thus, you will be sure you have the right size of a flow switch.
This factor will depend on the diameter of the pipe. The probes need to be at the center of the flow channel, where the flow is stable. Thermal flow switches are designed with two types of probes. Thus, when you know the insertion depth, you can select the correct water flow switch.
Upstream Straight Run
You already know that disturbance upstream affects the accuracy of the flow switch. Thus, you should assess the amount of flow disturbance and find a flow switch with higher resistance to disturbance. However, you should ensure that you minimize the flow disturbance as much as you can.
Power Consumption Measurement Method
When you introduce heat to the flow channel, there are two ways you can measure the heat. First, you can check the fluid heat difference at the two points. Then you can calculate the flow rate from the heat difference. In this method, you only have one power consumption point.
In the other method, you need to introduce heat at two points. The heat at the second point is applied to equalize the heat at the forest point. Thus, you will have two power consumption points. If you are after conserving power, then you will select the first type of flow switch.
All thermal flow switches have a user manual. You should check a switch that has a minimum installation restriction. The more the restriction, the harder it is to use the flow switch. Any wise buyer should select the flow switch that is easy to use. However, it would be best if you did not compromise on quality.
Water flow switches exist in many sizes and qualities. Also, you can calibrate them to different flow conditions. Select a switch that will fit in your industry and has a reasonable price.