How do I calibrate a DMT620M force transducer?

As a part of the general maintenance of the myograph, DMT recommends that the myograph is weight-calibrated at least once a month. The myograph should also be weight-calibrated every time the interface has been moved. Although lab benches are all supposedly perfectly horizontal, small differences in lab bench pitch can affect the calibration of the system. The myograph also should be calibrated if the system has been idle for longer than a month.

Force transducer calibration procedure
This section contains step-by-step instructions to calibrate the force transducer and should be used in conjunction with the steps described in Chapter 3 (FORCE CALIBRATION sub-menu under SETTINGS) of the user manual. A detailed description can also be found in the user manual. For older models the FORCE CALIBRATION might be slightly different, but the same principle applies.

  • Move the jaws/pins apart. If calibrating the transducer with the jaws in place, make sure a wire is mounted on the transducer-side jaw. If pins are being used, the wire does not have to be put in place. Fill the chamber with distilled water or buffer.Use the same volume that will be used during the experiments. Make sure the pins/jaws are properly aligned.

  • Set up the calibration kit (bridge and balance) on one of the myograph chambers as illustrated in Figure 4.6. When using the jaws in a wire myograph setup, the bridge arm should be placed in the small space between the jaw an the wire on the jaw connected to the force transducer, with the weight on the side of the force transducer at calibration. When using pin mounts, the bridge arm should be placed on the on the outside of the pin connected to the force transducer, with the weight on the side of the force transducer at calibration. In both cases, the bridge arm should be applying force toward the center of the chamber to mimic contractile force. These setups are shown below. The red dot is where the pin should be arranged, with the blue arrow indicating the direction that the bridge arm is applying force.  
  •  Turn the heat on. The weight should also be placed on one of the chambers during heating. The system takes about 20 to 30 minutes to reach 37°C. Placing the calibration kit and weight on the chamber allows them to warm up to the experimental target temperature. No need to bubble the chambers while waiting for the system to heat up.

  • When the system reaches target temperature, adjust the calibration kit so that the tip of the transducer arm is as close to the wire (if jaws are being used) or pin on the transducer side as possible without touching, as illustrated in the figure. One way to do this is to use the following technique. Start with the calibration kit in place so that the transducer arm of the bridge with the pans is not touching any part of the jaw or wire (if the jaws are being used) or not touching any part of the pins. Go to the main menu displaying the forces, and zero the channel being calibrated so the force reads zero. Slowly and gently slide the calibration kit forward toward the micrometer so that the transducer arm rests on the wire or pin, creating a force reading on that channel. Carefully slide the calibration kit back toward the transducer slowly until the force reads zero or very close to zero. At this point, as soon as the force reads zero, the transducer arm will be properly placed for weight calibration.

  • Go to the FORCE CALIBRATION sub-menu of the SETTINGS menu on the Interface to begin the actual transducer calibration. Follow the process that is described in the manualWhile calibrating the myograph system, record the calibration data into LabChart. This data will then be used for units conversion on the LabChart signal. 

Calibration procedure in LabChart (units conversion) 
  • Ensure that the wire on the transducer side has no force applied to it by the calibration bridge. (Note: the same principle applies when pins are mounted)
  • Start recording in LabChart, and follow the instructions in the myograph system User Manual for using the Calibration menu and placing the calibration weight. 
  • Once the force reading on the myograph system interface has stabilized and been entered, stop recording in LabChart. 
Repeat the above steps for any other force transducers that will be used. 

Next, perform the units conversion from volts to millinewtons (mN) in LabChart: 
  • In the Chart window, select the recorded calibration data. 
  • Select Units Conversion from the Channel Function pop-up menu to open the Units Conversion dialog box. 
  • In the Units pop-up menu, select Define Unit and type mN. 
  • Select data corresponding to the period when there was no force applied to the transducer-side wire, and click the Arrow button for Point 1. Enter 0 in the text box to the right. 
  • Select data corresponding to the period when the calibration weight was placed on the calibration bridge, and click the Arrow button for Point 2. Enter 9.81 mN (for the supplied 2 gram calibration weight). 
  • Click Apply and the units wil have changed from volts to millinewtons. The new units appear in the Units Conversion dialog box. 
  • Click OK to close the dialog box. The new units will appear in the Chart window. 
  • Repeat the above steps for any other channels on which you have recorded force transducer calibration data. 
  • Once all channels have been calibrated, save the document as a LabChart settings file. By using this settings file to start a new experiment, and then saving it with a new name, there is no need to repeat the above steps. (Note that a new settings file will be required if the force transducers are recalibrated.)

As of July 14 2017, ADInstruments no longer sells or supports any DMT products (unless previously purchased under tender contract). Instead, please contact DMT direct.