CMR Controls: Laboratory Airflow Control Systems

CMR Laboratory Airflow Control System

CMR Controls manufactures low pressure and air flow measurement and control systems for laboratories, clean rooms, microchip production plants, sterile suites and general purpose variable air volume areas.

Since the company was founded in 1978, many thousands of its pressure and air flow transmitters have been incorporated in vav and room pressure applications worldwide.

Main Features

Fast response time (milliseconds)
Building response time (1 second)
Adjustable face velocity 0.5 to 0.9 m/s or more
Actual face velocity measurement linear at any sash heigh
Pressure independent - face velocity is always controlled
Emergency exhaust panic button with adjustable set points

The systems consist of individual components which are compatible with any bms system.

Some CMR products are:

High precision face velocity sensors
Sash height position sensors
Sash access security locks
Laboratory safety pressure switches
Fume cupboard face velocity controls
Room supply/extract controls
Extract plenum controls
Stack velocity controls
High precision air flow measuring transmitters
0 - 100% speed controllable fans

System description

The CMR laboratory control system was designed to meet the high standards in safety for operators and to reduce energy costs substantially when closing the sash.

FC-controllers

The CMR fume cupboard (fc) controller is compact, factory tested and ready for installation by any controls company or fc manufacturers.

A nylon bulkhead fitting is normally fitted to either inner wall of the fc above sash opening height. CMR pvc white tube is connected to the bulkheads and to the negative port of the FC-controller. A CMR nylon bulkhead is fitted to the top of the fc, and red pvc tube is connected from there to the positive port of the FC-controller.

As the sash is opened or closed a relative air sample passes through the pvc tube from the top of the fc through the CMR FC-controller, where it is converted into an electric signal and scaled into m/s, and finally leaves via the two inner bulk heads into the extract system. The inner bulkheads are T-pieced together to provide an average suction through the CMR FC-controllers.The air sensing is on the clean side of the fc and cannot be contaminated.

The actual face velocity is then displayed on an lcd scaled in m/s. The display plate also incorporates high/low flow alarm, sash high alarm, emergency exhaust panic button and a facility to display the set point ie 0.5m/s.

In order to control the face velocity a fast acting CMR extract damper motor is fitted to the CMR exhaust damper thus keeping the face velocity constant regardless of sash height. The system is totally pressure independent.

The CMR FC-controller is fully software accessible and any parameter can be changed or information displayed on any pc via the CMR two wire bus. As an option the FC-controller can be supplied with a remote keyboard and lcd as well as a panel mount printer to provide the operator with additional facilities such as controlling power sockets (timed), monitoring the operators measuring transducers or monitoring operator experiments.

Operators presence sensors can increase airflows and an access key system can prohibit the use of the fc by others.

A sash height sensor can be helpful to monitor and control energy savings. The CMR speech annunciator can warn the operators of danger through preprogrammed voice recordings.

Room pressure control

Total Fume Cupboard laboratory extract system

The room pressure controller has a built-in room pressure transducer which is tubed to air probe plates in the ceiling and referenced to a neutral datum ie plant room. The set point is normally set at -5 Pa. As the sashes are being opened the room becomes more negative and the RP-controller either drives the fan inverter or supply damper to keep -5 Pa steady. The response time is milliseconds and hence excellent control is maintained.

When all sashes are closed a room exhaust damper ie air valve is controlled to keep the room at -5 Pa and to provide heating and cooling for the laboratory. The RP-controller acts as host computer and any FC-controller can be accessed via the keyboard to interrogate a fume cupboard ie sash position, resetting the setpoint of face velocities ie 0.50 to 0.95 m/s, muting alarms, etc. The host can also calculate air volumes and schedule the supply proportionally.

Plenum extract pressure control

The plenum pressure controller has a built-in pressure sensor for plenum or duct pressure measurement. In addition, a stack velocity sensor is provided and is connected to the CMR veloprobes fitted in the stacks. Normally a number of fume cupboards are ducted to a roof plenum. The PP-controller is tubed to bulkheads on the plenum and the plenum pressure is controlled to -165 Pa typically. In order to control the -165 Pa, a fresh air bypass damper is modulated. The stack velocity is normally kept constant by means of inverter control set to a manual speed. The PP-controller monitors the stack velocity and alarms in case of failure. As sashes are being opened and closed, the fresh air bypass dampers moves to fine tolerances to keep -165 Pa steady.

The PP-controller is connected to the communication bus and can be interrogated from any host. The CMR DM15 damper motor response in milliseconds is ideal for accurate plenum control.

PC communication

Any pc can be connected directly to any CMR MPC103 microprocessor controller on the network, the information can be distributed via the server to any point on the user's network.

Room pressure and plenum safety

The CMR PS-pressure switches safeguard the building and are normally set to 100 Pa for room pressure. In case of excess pressure the switches are hardwired to fans and damper control to provide safe emergency shut-down. The switches can be tailor-made for the client's applications. No building structure damage can possibly occur.

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