Constant Load Modes Available for Muscle Physiology Experimentation

 The Constant Load ModuleThe Constant Load Module offers three modes of operation, including:

  • Constant Load
  • External Loop
  • Bypass

This block diagram (right) graphically shows the three modes of operation in the Constant Load module.

Constant Load–This mode maintains a constant load on the tissue sample. SI-AOSUB Corrected Output, representative of the force transducer output, is the SI-COLUB feedback input. The SI-AOSUB Corrected Output is connected to the CL CMD (constant load command). An input pulse train from a data acquisition system (LabTrax 8/16) connects to the Capture BNC port on the SI-COLUB. This is an analog output from LabTrax 8/16 that sets the desired force applied to the tissue sample. When the capture signal is high, the force value applied as a position command to the motor allows the muscle sample to slack to the percentage of the force value set by the Force Step dial. When the capture signal is low, the position commands the tissue sample to re-stretch to the original force value.

External Loop– In this mode the SI-COLUB’s resources for controlling the motor are made available so you can specify an external signal (other than the motor/force transducer configuration) to be used as feedback. The SI-COLUB is constantly driving the motor position to affect the feedback signal until it matches a given command. The CL CMD input connects to an output on the data acquisition system (LabTrax 8/16) that provides the desired level of force (F0). This is the desired value that the feedback signal will be driven to achieve by changing the motor position output.

In order to get a true isometric muscle contraction, the sarcomere length must be kept constant during the contraction. For this purpose the output signal of the camera (SI-AOSUB) can be fed into the alternate feedback controlling the linear motor position using the SI-COLUB in External Loop mode. The alternate feedback system controls the linear motor so that the sarcomere length is held constant.

Bypass–In this mode, the Constant Load Module is completely bypassed. An output from the LabTrax 8/16 that drives the motor connects to the Bypass MOT CMD and then the MOT POS CMD OUT sends the same command directly to the Motor Controller.

IMPORTANT NOTE: THE SI-COLUB unit can only be used on tonically contracting muscle tissue (for example, during a tetanic contraction). For equivalent experiments in cardiac muscle and twitch type contractions, the Afterload software is needed. Contact WPI for further information.

Constant Load Mode–The CL Command receives a force measurement from the force transducer. If the capture command is issued, then LabTrax 8/16 captures the force and sets F0 to that force. LabTrax determines the set-point and the SI-COLUB calculates the Linear Motor command. The Linear Motor responds, and the force transducer takes a new reading. Then, the cycle repeats.

External Loop Mode–The CL Command receives a measurement from an external trigger. If the capture command is issued, then LabTrax 8/16 captures the measurement and uses it as the set-point. The SI-COLUB calculates the Linear Motor command. The Linear Motor responds, and the alternate feedback mechanism takes a new reading. Then, the cycle repeats.

 Bypass Mode–The Constant Load Module passes the motor command from the LabTrax 8/16 directly to the Linear Motor without making any calculations or alterations.