7
Instrument Description
Inspired by the need for a low-cost solution to the problems inherent in low resistance
measurements in the millennium, Valhalla Scientific developed the Model 4021 Digital
Ohmmeter. The 4021 uses a true "four-wire Kelvin" configuration in order to provide an accurate
resistance measurement down to 1 milliohm resolution. The wide range of the 4021 allows
measurement up to 1.9999 M
Ω
. Four-wire resistance measurement is explained in more detail in
Chapter 5.
The 4021 is available with a variety of test probes, accessories, and a BCD data output (see
Chapter 8). The 4021 is also capable of being operated from an internal heavy-duty battery pack
(optional). These items are explained in more detail in Chapter 4.
Safety Considerations
The Model 4021 is a very safe and easy to use device. Several items, however, are worth
mentioning in order to obtain maximum utility and safety from your instrument.
1) For AC instruments always use the three-terminal power cord provided or its exact
equivalent. The 4021 requires a continuous ground connection for proper operation. If using
an extension cord, ensure the ground connection is continuous throughout the extension.
2) For battery-operated instruments, use only the adapter provided or its exact equivalent. The
batteries may be damaged by excessive charging currents.
3) The fuses for both AC and battery operated instruments are for the safety of the user as well
as the instrument. Always replace blown fuses with their exact equivalent
only
!
4) If testing large inductive devices such as transformers, avoid drawing an arc when connecting
or disconnecting the leads. This is best accomplished by selecting the highest resistance
range (2M
Ω
) before making or removing connections.
Instrument Identification
Valhalla Scientific instruments are identified by a two part serial number. The Serial Tag is
located on the rear or bottom of the instrument. The number is in a form of 00-0000. The first
two digits, called the serial number prefix, indicate the model. It changes only when a change is
made to the instrument. The last 3 or 4 digits, called the serial number suffix, are unique for each
individual unit.
Be sure to include the entire serial number, both prefix and suffix, in any correspondence about
your instrument.
The serial number can also be found on the Main Board, Calibration Tag and Certificate of
Calibration.
