A step-by-step demonstration of how to calibrate a Force Transducer and apply a pre-tension for measuring isometric contractions in an isolated tissue study.
- Force Transducer
- Micropositioner + Stand
- 10g weight
- Bridge Amp
- Computer with LabChart Software installed
Before recording any signals, it’s important to set up your data acquisition equipment correctly.
- Attach the Force Transducer to the Micropositioner + Stand
- Connect the Force Transducer to the Bridge Amp
- Connect the Bridge Amp to the PowerLab
- Lastly, connect the PowerLab to your computer and open LabChart
Zeroing the transducer
The next thing you need to do is zero the force transducer.
- In LabChart, click on the channel name that the Bridge Amp is connected to and select ‘Bridge Amp’ from the drop-down menu.
- In the Bridge Amp Dialog make sure that the range is sufficient for the forces you will be recording. In this case, 10 mV will be fine.
- Next, zero the transducer by clicking ‘Zero’. This will take a couple of seconds, make sure that the transducer is not moved during this period.
- Once that is done, click ‘OK’
Calibrating the transducer
Now that the transducer has been zeroed, you are ready to calibrate the transducer.
- First, start the recording in LabChart by clicking the ‘Start’ button
- Because the force transducer has just been zeroed, we know the current reading on-screen (in mV) is equivalent to 0 grams. Enter a comment labeled ‘0’ into LabChart to mark this section of the recording.
- Next, hang a small weight of known value onto the end of the transducer. In this example, we are going to use a 10-gram weight. Once on, add another comment to the recording labeled 10.
- Click ‘Stop’ to stop the recording
- Make a selection of the recording between the two comments by clicking and dragging the mouse across the recording.
- Click on the Channel name and go to ‘Units Conversion. The Units Conversion Dialog will display the recording that was selected (see image below).
- Select an area of the recording that represents the first reading of 0 grams in the preview window.
- Then click the arrow next to Point 1 and the voltage for that reading will be entered into the left-hand box.
- Next, type in the value this selection represents in the right-hand box (in this case, 0).
- Repeat the above steps for the second reading of 10 grams, next to Point 2.
- Make sure the units are set as grams, then click ‘OK’.
- Now your force transducer is calibrated in grams
Applying a pre-tension
Another factor you might need to consider when doing a tissue contraction study is whether you need to apply a pre-tension to the tissue before making any recordings. The exact pre-tension (in grams) should be specified in the protocol.
To apply a pre-tension:
- Loosely hang the tissue on the transducer. One end of the tissue should be tied to the transducer and the other end to the tissue hook in the bath.
- Start the recording. The reading on-screen will have already increased slightly due to the added weight of the tissue on the end of the force transducer.
- Adjust the micropositioner by twisting the knob on top. This will slowly to lift the force transducer and increase the tension on the tissue.
- You can view the exact amount of tension that is being applied to the tissue in grams using the DVM readout in LabChart.
- Once the desired pre-tension has been reached, open the Bridge Amp Dialog and zero the transducer again by clicking the ‘Zero’ button.
- Once zeroed, click ‘OK’ to return to the recording.
- Now you are ready to begin your experiment!