POLaRControls

Embedded Systems and Monitoring

Design Features

AC and DC Motor Drives:

PCI's engineers have been involved in designing fractional horse power AC and DC motor drives for over 12 years. AC drives include shaded pole, split-capacitor single phase, and three phase induction motors. DC drives include half-drives, single phase, three phase, and sensorless three phase drives.

Air Flow, Temperature, and Humidity Sensors

PCI manufactures our own air flow sensor that is based on hot wire anemometer principles. This device has both an analog output and a digital network interface with its own identification address. It is compact and low cost, relative to other sensors on the market.

PCI uses temperature and humidity sensors from approved sources, whose products meet a number of criteria including stability, reliability, and low cost.

Customized Power supplies:

It is common to integrate power supply technology in the field of thermal management. This accomplishes several important functions including motor speed control, EMI and conductive noise control, voltage clamping, and current in-rush protection. PCI's engineers have experience in the design of linear and switch mode power supplies, both isolated and non-isolated, with power factor correction and EMI and conductive noise issues.

Embedded Microcontroller:

The use of an embedded microcontroller to control and monitor thermal enclosures has greatly increased system reliability and performance. The microcontroller can create a precise functional relationship between sensor input and controllable variables, such as fan speed. This feature insures uniform performance among a large number of systems. The microcontroller makes available performance features that would otherwise be prohibitive due to cost and complexity. These include fan synchronization, the implementation of sophisticated control algorithms, the use of multiple sensors, data logging, remote access of information, upgrades in software rather than hardware, and hysteresis of trip points.

Fan Degradation Monitoring:

When an air mover's operating parameters (applied voltage, running current, speed) and system performance parameters (airflow) are known, it is possible to make a determination of the relative operating efficiency of a motor. This information can be used as a rough measure of the remaining life of the motor.

A second approach simply involves recording the run time history of the motor. This approach is useful because motors tend to have a predetermined life, with a life expectancy rated in running time.

Fan Synchronization:

Fan assemblies offer a number of benefits when used as air movers, including low cost, system redundancy, and good air flow distribution. Each of these features requires embedded intelligence to be fully realized, usually in the form of a low cost embedded microcontroller. The microcontroller performs several important functions. The first of these is fan synchronization, where all fans run at the same speed. This reduces cross flow and beating. It creates a more uniform flow area and increases the efficiency of the system. In the process of controlling the fans the microcontroller is also monitoring them. If one fan fails, the microcontroller can run the others at a predetermined speed to compensate, as well as send an alarm indicating the failure of a fan. This function greatly increases system reliability.

Another important feature of the microcontroller is the ability to precisely control the fan speed as a function of an input, such as temperature, airflow, or pressure. This feature insures that the thermal performance of the system determined during the design stage is accurately reproduced on manufactured units.

Filter Blockage Detection:

There are two common air flow conditions where detection of air filter degradation or blockage occur. The first is flow generated by a constant speed air mover. The second is flow generated by a variable speed air mover. Different strategies and costs are involved depending on the flow rate and level of accuracy required.

In the constant speed air mover case, only one parameter is required, which is a direct indicator of the impedance of the filter. An increase in the filter impedance due to reduced porosity leads to an increase in the pressure drop across the filter, and to a corresponding decrease in airflow. Both of these parameters can be used as an indicator of filter status. Unfortunately, the measurement of these parameters can have a large dependence on the positioning of the sensor and on other tolerances that exist among different systems. A technique that greatly increases the accuracy and eliminates inter-system dependence is to have each sensor calibrated after installation. PCI's filter blockage modules all have this feature.

In the second case where the air mover speed is variable, a second parameter is required to accurately measure filter impedance. Parameters that can be used include airflow, differential pressure, and fan speed. The fault setting is no longer a point but a line (straight or curved) dividing a fault and non-fault region. A low cost micro-controller with non-volatile memory can be used to calibrate the fault line based on 2 or more trip points using the 2 specified input parameters. PCI has many years of experience designing this type of component either in a stand alone form or as a component of a larger system.

Networking:

In applications that require distributed functions, such as inter-connecting sensors, actuators, or controllers throughout a room, the ability to connect each module to a network is essential. PCI has experience with several different network platforms, the interface of which can be incorporated into each component. Bus extender chips and error correction code schemes are utilized to help create a robust network.

PID or Fuzzy Logic Based Control:

A PID (proportional, integral, derivative) algorithm is typically used in systems with a single input and single output. Often, systems with multiple inputs, such as the existence of several exhaust temperature sensors, can be reduced to a single value. For example an average of all sensors can be used, or the reading of the hottest sensor.

A Fuzzy logic based servo system can be designed effectively in systems with several types of inputs. An example would be a system that servo's the airspeed in conjunction with maintaining an average inlet/exhaust temperature profile.

Remote Access:

One of the primary functions of an embedded controller is to process information and to reduce it to some output format which serves as an input to some other system. However, it is useful to be able to extract the raw data out of the controller, and also to be able to adjust its operating parameters remotely. Many of PCI's controllers include a digital interface (I2C, RS-232, CAN, LAN) which permit such control.

System Redundancy:

Using multiple air movers protects against a single air mover failure. To protect against a component failure on the control board, an additional circuit, which operates in the background and is electrically and operationally independent from the primary controller, is included. If a fault is detected, it activates, overriding the main controller and operating the system in a safe mode. This usually consists of running the fans at full speed and sending an alarm indicating that the main controller has malfunctioned.

User Programmable Parameters:

This feature allows the operating parameters to be adjusted outside of the factory where the unit was manufactured. The parameters are stored in non-volatile erasable memory rather than in the code, which would require recompilation at the factory. Storing the parameters in this way enables the performance of the controller to be adjusted for different applications. It is useful for testing purposes during the design phase, or as an upgrade to an existing system. It facilitates system design by allowing for different configurations during development. It reduces cost by allowing the same hardware to be used for different programs. It reduces risk by allowing operational changes to occur without having to replace hardware.