Electrical Engineering Asked by handle on December 4, 2021
The MAX14821 (datasheet) is a 24 V IO device that features selectable current loads for use in actuators
on the inputs.
What would this be used for? It’s not just to load a 24 V “high” signal coming from a PNP-logic output, i.e. pull the input down of there’s no signal? If it were, where’s the equivalent high side current source for use with NPN signals?
PLC Standards Compliance Ensures Future-Proof Solutions
( two slightly different stds )
IO-Link Versions 1.0 and 1.1.2
IEC IEC61131.9 SDCI
Selectable means USA or EU stds for C/Q IO interfaces. (clk & data high voltage long wire bus standards)
Optional 6mA/7mA Current Loads at Both 24V Inputs is the selection
For use with hi-side logic in 500m communication buswire pairs up to 400Kbaud ??
ie. 4k load to ground from 24V/4k = 6mA
e.g. IEC 61131 Type 1 uses 7mA with noise margins that @Arsenal pointed out for Type 2
Ref: IO-Link is the first standardised IO technology worldwide (IEC 61131-9) for the communication with sensors and also actuators. http://io-link.com/share/Downloads/At-a-glance/IO-Link_System_Description_engl_2013.pdf
A logic "1" is defined by the received voltage from a defined current in a selected load resistor to ground. If IO link is 6mA * 4k =24V then IEC611131.9 is 7mA * ?? .... and the thresholds are used for noise margins.
If you search hard enough you can read all the IEC standards free.
http://www.plcopen.org/pages/tc1_standards/ what each dash number means
Answered by Tony Stewart EE75 on December 4, 2021
Their reasoning:
The C/Q and DI inputs have selectable current sinks that can be enabled for use in actuators where the master requires a Type 2 load.
What is a Type 2 load?
I'm not so sure on this one, but the hint I found was on the Pepperl and Fuchs page:
Switching point according to DIN EN 61131-2 (Type 2)
0 (unattenuated) ≤ 3 mA
1 (attenuated) ≥ 5 mA
I don't have access to the DIN EN 61131-2, so I cannot give a more detailed explanation. Seems like there is a digital input standard related to current and 7 mA seems like a safe number to make something go high.
Answered by Arsenal on December 4, 2021
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