The Digitimer two or four channel D440 amplifiers provide versatile, low-noise, multi-channel amplification and filtering systems for human isolated EMG studies. Primarily developed to provide a human-safe, isolated amplifier suitable for nerve excitability testing in research applications, the D440 has proved an attractive option for researchers wanting to employ basic EMG measurements in a variety of areas.
Common Mode Rejection Ratio – Now Improved
In the last year, Digitimer engineers have updated the D440 design, greatly enhancing the Common Mode Rejection Ratio (CMRR) of these amplifiers. This is important because it is the CMRR that determines how good an EMG amplifier is at rejecting signals that are picked up by both the Active and Reference recording electrodes. In most cases the dominant common mode signal will be mains interference, which can be picked up from multiple sources within the room an EMG recording is made.
Usually, by following good recording practices, such as rigorous skin preparation, high quality, impedance-matched electrodes and sensible cable routing, it is possible to reduce electrical interference to an optimal level. However, we have been made aware of a few cases where 50/60Hz noise could not be removed through use of standard recording practices or replacement of faulty electrodes/lead wires. This phenomenon is typically seen when recording electrodes have impedances that vary significantly and having examined the D440 design and our in-house calibration procedures, we made some adjustments that make the D440 amplifier less sensitive to this type of electrode imbalance.
Serial number label showing no Mod. States have been implemented.
An Invitation to Upgrade Your D440
If you have an older D440 amplifier that has not already been updated to “Mod. State 1” and are experiencing persistent problems with 50/60Hz mains frequency noise which is impossible to eradicate, then we suggest you make contact with us or your local Digitimer representative in order to arrange to have it serviced and updated to the latest Modification State. On the serial number label, the Mod. State number is indicated by the highest number blacked out within the numbered boxes. In the example shown above, no modifications have been made, therefore this unit would be Mod. State zero (unmodified) and eligible for an upgrade. Please note that any D440’s returned to Digitimer for a routine re-calibration and safety check within the last 6 months have been updated to the latest mod. state.