Screening Services & Training LLC
25092 Natama Ct Based upon a procedure written by Screening Systems, Inc.
Laguna Hills, CA 92653-5607
How to: Lower the Chamber Operating Range to below –60 degrees C on SSCTM-2000 Systems
This procedure applies to systems manufactured by Screening Systems, Inc. that use the model QRSTM-2000 vibration controllers.
The temperature low limit for some model QRSTM systems is set to -60° C. To lower the limit below this value on systems controlled by the SSC-2000 controller requires a few steps be accomplished to assure proper system operation and integrity.
The first step is to lower the Chamber Absolute Temperature setting in the System Configuration. From the main menu across the top of the screen, select “Configure” then “System” from the resulting pull-down menu. The following window will appear.
Change the circled parameter to the lowest temperature to be set or programmed during the test. The lowest value that can be set is –100 degrees C. To avoid errors, however, it is recommended that the setting not be any lower than necessary for a particular test.
After selecting “EXIT (F1)” and saving the changes, adjust the system’s independent Low Temp Limit device located on the front panel of most systems.
The limit detector shown above, Honeywell UDC 2000, has two adjustments that must be changed. The first limit is adjusted by changing the “Setpoint” value 10 to 15 degrees lower than the lowest value that will be programmed. When this limit is exceeded the redundant LN2 valve is de-energized until the detector is reset.
To change the “setpoint”, push the “Display” button on the Low Temp Limit device and use the down and up arrow buttons to select the desired value.
The second limit within this device alerts the computer controller that this temperature limit has been exceeded.
This action results in an audible warning along with a red visual warning on the controller screen indicating that an external temperature limit has been exceeded. In addition, the controller command to the LN2 control valve is set to zero so no more cooling is called for. This second limit is usually set between 5 to 10 degrees lower than the lowest value that will be programmed.
To change this limit, push the “Set Up” button until “ALARM” shows in the display. Then push the “Function” button until “A1S1VA” is shown in the display. Using the up and down arrows, adjust the setting to the desired value. To enter the new value and return to the top display, push the “DISPLAY” button once. To leave the value unchanged, push the “RESET” button once and then the “DISPLAY” button.
An alternate limit detector, RKC Instruments, Inc. Model CB900L has a single limit that both turns off the LN2 valve and alerts the computer controller when the low limit is exceeded.
To change the low limit on this device starting from the PV/SV display, push the “SET” button once. Press the “left arrow” button until the desired integer is highlighted then push the up and down arrows to change the integer. To accept the new setting and return to the PV/SV display, push the “SET” button 3 times.
The final step in the procedure is to install or verify the installation of a thick table mat. The purpose of the mat is to protect the table from the extreme cold and to decrease the LN2 consumed during a test. An additional benefit of the mat after a cold soak is to decrease the amount of warm-up time required before the doors can be opened without causing condensation to form on the table surface.
This completes the procedure.
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