What are Decade Boxes?
Decade boxes are test instruments which use a series of resistors, capacitors, or inductors to replicate different electrical values. They can be quickly and easily substituted into a circuit and replace any standard value component. Their ability to be configured to nearly any resistance, capacitance, or inductance makes decade boxes a convenient way to find the optimum value for circuit operation. They are ideal for verifying the accuracy of test equipment prior to use as well as troubleshooting.
They are known as decade boxes because they have controls that correspond to the digits in a decimal number - a control for the tens position, a control for the hundreds position, and so on.
How they work?
Decade boxes are passive devices that consist of switches and either a series of resistors, capacitors, or inductors of different values arranged to form decades. Decades are set up in factors of ten. For example, a resistance decade box may have a 5 ohm, 2 ohm, and two 1 ohm resistors in the first decade. The second decade may have a 50 ohm, a 20 ohm, and two 10 ohm resistors. The third decade may have a 500 ohm, a 200 ohm, and two 100 ohm resistors. With this combination, this three decade box can be switched to any value from 1 ohm to 999 ohms in 1 ohm steps. Some decade boxes may have 6 or more decades to allow for very wide ranges and highly precise values. Decade boxes are characterized by their range, maximum resolution, and accuracy.
Using a decade box for testing consists of setting the box to the desired value and hooking up the input device such as a transmitter, controller, multimeter, etc. The display value of the input device should match the set value of the decade box.
Types of Decade Boxes
Resistance Decade Boxes – can simulate resistance for testing the accuracy of thermostats, temperature controllers, multimeters, and others.
Capacitance Decade Boxes – can simulate capacitance for testing the accuracy of multimeters and other instruments that measure capacitance.
Inductance Decade Boxes - can simulate inductance for testing the accuracy of multimeters and other instruments that directly measure inductance
Field and laboratory work
Things to Consider When Selecting a Decade Box:
Is this for simulating resistance, conductance or inductance?
What range is required?
How much resolution is needed?
What level accuracy is preferred?