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In the last article, we discussed the importance of speed control and using a controller in a fan cooling application. Speed controllers can range from a simple potentiometer with manual control to more complex devices used in closed loop systems.
It is important to evaluate the environment the equipment is subjected to in order to select an appropriate controller. Open loop systems are better suited for applications where there is flexibility of operation, closed loop systems are generally preferred if a known set parameter needs to be maintained (e.g. 25°C at all times).
The Thermal Management System (TMS) is the ideal solution for both, as it can operate as an open loop or a closed loop system.
But what is a TMS?
A TMS is a temperature based DC powered controller, designed for use with 4 wire speed controllable fans. Although originally designed for purely DC supply applications, it can now also be used with EC fans as long as a separate power supply is provided.
It works with a graphical user interface via USB connection, and it can control up to 4 fans at the same time. Each of the fans are able to have an independent profile which is useful when different fan types are used in the same application, or if they are situated separately within the equipment.
One of the main advantages is you can fully configure and modify the control profiles, which is a perfect tool for designing tailored solutions.
An example of an open loop system is shown on the image below.
- A fan profile is selected for the modification settings.
- A thermistor input is selected (2 available).
- Two set temperatures are chosen (maximum and minimum) with a respective speed.
- A linear response between both points is automatically generated.
This is a general set up which needs little information to create an effective profile. However, for greater accuracy the “multi point” option can also be used.
This feature allows the configuration of eight set parameters as opposed to two, which will generate a non-linear response. It can be particularly advantageous when approaching critical conditions, as a greater speed increase ratio might be required.
Alarm conditions – What if?
Every application will eventually experience conditions that will challenge the equipment’s normal operation. Whether it is a fire affecting the equipment or an open door during routine maintenance, a reaction from the fans is required. Using the TMS these conditions can be defined, and the corresponding reactions configured.
A total of 4 alarms can be set, and multiple conditions can be defined in each profile. This is best seen in the example below.
First, the criteria for the alarm condition is determined. In this case:
- Any fan failure, thermistor failure or temperature rising above 50°C in any of the thermistors will be classed as an alarm condition.
Then, the desired reaction from the fans is defined. In this case:
- All fans will operate at full speed (100% PWM) if any of the above conditions is met.
Each alarm will have a different priority so it is crucial to make sure the most extreme conditions are configured first. A fire will no doubt be more important than a fan fail!