A Typical Constant Load Experiment

The SI-COLUB Constant Load Module for performing constant load experiments, has augmented flexibility. In its primary mode (Constant Load) the unit takes an external trigger command from the force transducer to perform a constant load cycle. In addition, the module allows for a different external trigger, or you can completely bypass the module without having to switch cabling.

The SI-COLUB Constant Load Module lets you maintain a constant force, muscle length or sarcomere length rather than keep the total length of the preparation constant during an isometric contraction. This is accomplished using a feedback loop.

The SI-COLUB monitors a designated parameter to determine how much force is necessary. It also monitors a feedback signal. The motor position command signal driving the motor is constantly adjusted to drive the feedback signal to the commanded set-point.

In its simplest form, you use the MDAC software to create protocols for muscle experiments. MDAC controls the LabTrax 8/16 data acquisition system which in turn sends commands to the SI-COLUB Constant Load Module.


A Typical Constant Load Experiment


The position protocol from the LabTrax 8/16 data acquisition system sends commands to the SI-COLUB which drives the motor to apply force to the tissue or release force on the tissue.

In this type of experiment, the tissue is held at an initial position. The tissue is stretched using the muscle research platforms manual adjustment until the desired initial position is reached. MDAC sends commands to establish the intended target force to be maintained on the muscle tissue (F0). At this point the SI-COLUB is issuing a fixed position command to the motor causing it to remain stationary.

When the muscle is stimulated, it begins to contract, and the force increases. After the desired force is reached or a predetermined time has elapsed, a trigger pulse is issued by MDAC to the SI-COLUB that causes it to take a reading of the force at that time (F0). Feedback of the actual muscle force, provided by the force transducer (via the SI-BAM21-LCB or SI-AOSUB is fed into the SI-COLUB where it is analyzed.

When the SI-COLUB is triggered, the SI-COLUB sends a command to the Linear Motor Controller to allow the muscle to slack until the muscle exerts a force that is equal to F0 times the percentage value on the Force Step dial (kF0). The time it takes to reach this force is determined by the Slack potentiometer.

The SI-COLUB sends motor position commands to maintain the kF0 force until the desired time has elapsed and LabTrax 8/16 sends another stretch signal to return the trigger signal to its original state. This causes the SI-COLUB to stretch the tissue back to its original position/force (F0).The restretch time is determined by the Re-stretch potentiometer.

The SI-COLUB offers three modes of operation: Constant Load, External Loop and Bypass. For information on these modes, see Constant Load Modes.

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