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Goals and Symptoms
In certain cases a device that is connected and triggering the digital inputs on an ION7650 or ION7550 can have a leakage voltage. A leakage voltage is occurs when a device produces a certain amount of voltage across its terminal when it is open (ideally the value should be 0 volts).
In the case of a device triggering a digital input: when the device closes the circuit the digital input registers a trigger, and when the same device opens the circuit the digital input should not be registering a trigger.
But in the case of a voltage leakage (when the triggering device is open) some testing is required to determine the results.
Facts and Changes
input doesn't open
Causes and Fixes
The internal resistance between the Scom and S8 or S7 in the diagram below is 230K, while on the old 7550/7650 (before September 2009) meters it was 40K.
The minimum amount of current required for the meter at the digital inputs to register a pulse is 50 micro A.
Hence with this information, figure out if a leakage voltage across the digital input connection is enough to produce a 50 micro ampere current. If the leakage produces a 50 micro ampere current or more work out the circuit to reduce the current.
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Date Created: August 10, 2009
Last Revised: August 21, 2009
Original Author: SN
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