Designing an automatic test system’s switching needs an understanding of the signals to be changed as well as the test to be performed.
The most appropriate switch cards and methods to use in applications that entail switching voltage signals will depend on the size and impedance of the voltages involved.
Mid-Range Voltage Switching
Mid-range applications (1V to 200V) frequently involve switching a voltmeter or voltage source to multiple devices, such as testing batteries, electrochemical cells, circuit assemblies, and thermocouples.
Changing a Voltmeter to Multiple Sources in Series
When switching a voltmeter to a series string of 30 voltage sources (VS), to prevent short-circuiting one or more of them, always open a given channel before closing the second one (break-before-make operation). Additionally, add fuses in series with each voltage source and avoid exceeding the card’s common-mode score. In a typical instance, each source is 12V and the complete voltage across the string is 360V.
Switching a Voltage Source to Multiple Loads
When using a single voltage source connected to multiple loads, if a couple of loads are connected to the source, the voltage at each load may be less than expected due to current flow through the common impedances (R), like the test leads and trace resistance. check out the list of all China Relay Socket Manufacturers, Factory, Supplier – provides Cheap Relay Socket Exporter & Wholesale and also a most up to date website.
When switching a voltage source to multiple devices, it may become necessary to compensate for voltage drops due to change resistance. In particular, if the devices have low resistance, the current flowing through the switches might cause a significant voltage drop.
Low Voltage Changing
Special techniques can help prevent voltage errors when switching signs of millivolts or less. These errors could be caused by thermoelectric offset voltage in the card and connecting cabling, change film contamination, magnetic interference, or ground loops.
Thermoelectric Offset Voltage
A low voltage card’s key specification is its contact potential or thermoelectric offset voltage. Thermoelectric voltage is the voltage generated by thermal differences at the junction of dissimilar metals, such as between the nickel-iron reed relays and the aluminum conductor to which they’re connected.