[Table of Contents]
People old and young
enjoy waxing nostalgic about and learning some of the history of early electronics. Electronics World was published
from May 1959 through December 1971.
As time permits, I will be glad to scan articles for you. All copyrights (if any) are hereby
component datasheets can be pathetically lacking in detail for parameters
that you might think would be a minimum amount of information needed
in order to integrate the device into a circuit or system. Or, it may
be that you found a part in a spare parts box and can't find a datasheet
for it. When those times come, it is necessary to characterize the part
yourself. Relay control really isn't rocket science when it comes to
electrical circuits, but there are a few rules of thumb that should
always be observed, the most important of which (other than not exceeding
voltage and current maximums) is to wire a diode reverse biased across
the coil terminals so that the voltage/current induced due to the field
collapse during de-energizing does not smoke the driver circuit.
This article from the April 1967 edition of Electronic World recommends
a test setup for determining the cut-in and cut-out speeds. It might
be important to know the speed in case the application has a timing
requirement for synchronization with another part of the circuit/system.
Here are links to the other relay articles:
Operate and Release Times of Relays
Finding Relay Operate and Release Times
Arc, Surge, and Noise Suppression
See all the available
Finding Relay Operate and Release
By Donald Ludwig
When designing circuits using relays
it is often necessary to know the relay's operate and release times.
Because of certain circuit conditions, the times given by the manufacturer
will not always hold true. The method to be described will help establish
these parameters and requires only a regulated power supply, a single-trace
oscilloscope, and two simple circuits - as suggested by the National
Association of Relay Manufacturers. This article illustrates the standard
s.p.d.t. break, make Type-C relay under test. This type of relay is
frequently used and the circuits employed can easily be converted to
test other types of relays.
Operate time begins when the energizing
voltage is applied to the relay coil and ends when the wiper arm has
reached the energized (N.C.) position. See Fig. 1. Release time starts
with the removal of the energizing voltage from the coil and ends when
the wiper arm has returned to the de-energized (N.C.) position. See
Fig. 1. Circuit used to find operate time of relay along with oscilloscope
display that is produced with setup.
The checks should be made under conditions closely approximating
actual operating conditions. These include temperature, mounting position,
use of arc suppressors, and any other circuit conditions that may affect
operate and release times. It should also be remembered that the accuracy
of the test is dependent on the accuracy of the scope, if all other
precautions are taken.
If the relay being tested has more than
one set of contacts, the operate and release times of each set being
used should be checked. The time required for each set of contacts to
function may differ from one set to another. An increase in coil temperature
due to repeated operations of the relay may cause the resistance of
the coil to change and affect the time elements of the relay. Each set
of contacts should be checked several times before calling the test
When determining relay operate and release times,
the scope's sweep speed should be set with a time base which will permit
viewing of the waveforms and still allow accurate readings to be made.
This method requires no elaborate equipment to establish
the relay's operate and release times. Using an oscilloscope also permits
contact bounce to be examined.
Fig. 2. Circuit used to find release time of relay. The values of CLR
and Vc depend on particular application.