Recording Experimental Signals > Zero levels
The signal zero level for a channel can be defined in either of two ways. In From record mode, it is computed as the average level from a defined portion of each record. In Fixed mode, it is fixed at a level defined by the user and does not vary from record to record.
From record mode
Use the from record zero mode when you want to measure transient signals, which are superimposed upon a baseline level which may be varying from record to record. To set the zero level from a portion of the signal record itself in from record mode:
1) Move the mouse pointer over the horizontal zero level cursor of the channel you want to change. (The mouse pointer turns into an up/down arrow.)
2) Slide the mouse pointer horizontally until it overlies the region of the record which is to be defined as the zero level.
3) Click the right-hand mouse button to open the zero level dialog box.
4) Select the From Record option.
5) The zero level is computed, for each record, from the average of a series of (default=20) samples starting at the sample indicated in the At sample box. If you want to change the number of samples averaged to compute the zero level, change the value in the No. averaged box.
6) Click the OK button to use the new zero level.
Fixed Level mode
Use the fixed level zero mode when you want to make measurements relative to a fixed absolute level. To fix the zero level at a constant value to be used for all records in the file:
1) Move the mouse pointer over the horizontal zero level cursor of the channel you want to change. (The mouse pointer turns into an up/down arrow.)
2) Hold down the left mouse button and drag the zero level cursor vertically until it is at the desired level.
3) Click the right- mouse button to open the zero level dialog box.
4) Select the Fixed option. The vertical position of the fixed baseline is indicated (in A/D converter units) in the Level box. You can set the zero level by entering a value.
5) Click the OK button to use the new zero level.
Fixed mode is typically used for the membrane potential measurements in voltage/patch clamp studies of voltage-activated current.(Note. Entering a value of zero into the Level box sets the zero level to the true zero voltage level for the channel)