Written by: Dan Weise
Recently, I was helping a customer troubleshoot the analog input on his Siemens MultiRanger 200.
For common troubleshooting, using voltage values to confirm a zero, mid point and span is all that’s needed. I find it easier to put a voltmeter across the analog input and read the voltage drop than to wire an amp meter into the circuit to read directly, but that assumes that the analog input’s resistor value is a known. For the most commonly used input resistance (250 ohms), the equivalent voltage drop is 1.0 to 5.0V.
Being the guy who actually reads the user manuals, I looked in the Siemens manual to find the input resistance, and it’s not there.
So I put a calibrator on the analog input of our shop demo unit and measured a 1.0 to 5.0V drop over 4.0 to 20.0mA input, which makes the MultiRanger mA input resistor a conventional 250 ohm resistor. That’s good to know if you deal with HydroRangers or MultiRangers.
By the way, an analog input resistance is by no means always 250 ohms. I have run across 1, 2.5, 5, 10, 50, 62.5, 100, 150 ohms as values for analog input resistances as some of the screen shots below show:
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Lesman Instrument Company is the authorized Siemens representative in Illinois, Indiana, Missouri, Paducah KY, Wisconsin, and Michigan’s Upper Peninsula. If you are located outside that area, you can find your local sales office or get technical assistance by calling 800-365-8766.
Dan Weise, Lesman product specialist, is an instructor for training classes on process instrumentation hardware, software, and technology.
Dan has been involved in all facets of data acquisition and process instrumentation since 1978, from sales and commissioning to service and support. He’s a long-time member of ISA, and has been with Lesman since 1988.
In his words, Dan’s the guy “who reads all the manuals nobody else reads”. In Lesman customers’ words, he’s the trainer to call if you want to “cut to the SO WHAT of instrumentation”, so it’s easy to understand.