I was looking for the concept of "Full-scale error" (related with laboratory measurement terminology) on the web without success. I would appreciate your help.
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\$\begingroup\$ I just Googled "full scale error", got some 85 million hits, and just a cursory glance at the first page showed some good stuff. \$\endgroup\$– EM FieldsCommented Oct 10, 2015 at 12:44
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3 Answers
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An error expressed as a percentage of full scale means that any measurement made will fall between the limits given by that quantity.
For example, an analog voltmeter with a range of zero to 100 volts specified as having an accuracy of +/-1% of full scale can be off by plus or minus 1 volt when there's between zero and 100 volts across the meter.
So, with the meter reading 1 volt, the actual input could be anything between zero and two volts, and with the meter reading 100 volts the actual input could be anywhere between 99 and 101 volts.
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\$\begingroup\$ why is it better to state +/-1%FS , than simply say +/-1Volt ? \$\endgroup\$– nassCommented Oct 9, 2015 at 14:53
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\$\begingroup\$ I don't believe it even came up, let alone being touted as "better". \$\endgroup\$ Commented Oct 9, 2015 at 16:22
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\$\begingroup\$ i am looking for the reason why companies may choose to state the error in one way or the other... \$\endgroup\$– nassCommented Oct 10, 2015 at 11:39
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\$\begingroup\$ Probably because that's the way it's done, and everyone - Well, almost everyone - understands what it means. \$\endgroup\$ Commented Oct 10, 2015 at 12:36
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\$\begingroup\$ there is definitely a reason other than "it has existed like so". \$\endgroup\$– nassCommented Oct 10, 2015 at 15:40
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The definition varies a bit, but often it must be added to a 'zero' error, and unless otherwise specified, applies only under reference conditions- warmed up for 1 hour, ambient temperature 20°C +/-1°C or whatever. Temperature changes to scale and zero, and aging often must be added on top of that. In the case of thermocouple instruments, the cold-junction compensation is added on top (and may be specified as a ratio such as 20:1, meaning a 20°C change in ambient temperature could cause an additional 1°C error).
An error specification of 1% F.S. means that if the scale is 4mA to 20mA, that error will not exceed +/-160uA (1% of the full scale deflection, which is 20mA-4mA = 16mA). If they're complete d*cks it could mean +/-2uA error, as I said, definitions vary.
So if the measurement is at mid-scale (12mA) then that error could be +/-2% of reading.
answered Aug 2, 2014 at 22:25
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\$\begingroup\$ I think you mean the 'error will not exceed +/- 160uA '- right? \$\endgroup\$– efox29Commented Jun 5, 2022 at 20:44
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\$\begingroup\$ @efox29 Yes, thanks, corrected. \$\endgroup\$ Commented Jun 5, 2022 at 21:53
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As an example, an error of 10 mV in a full-scale deflection of 2V would be a "full-scale error" of 0.5%. In other words you compare the error with the limits of measurement of the device and express that as a percentage.
