Instrumentation: Terminology for guard terminals. What do you call them? - Page 1
Forum section: electronics / projects

author: Cerebus
author_rank: Super Contributor
timestamp: June 13, 2017, 06:45:23 pm
content: It's common on many electronic instruments (SMUs, DVMs, electrometers, picoammeters, LCR bridges, etc.) to have a guard terminal, sometimes a passive guard and sometimes an active, driven guard. Some instruments have both (e.g. some LCR bridges, many SMUs) but I've never seen an instrument that explicitly brings both guard types out as individually labelled terminals - those kind of instruments usually have the guard on the secondary shield of a triaxial connector (e.g. Keithley 236 SMU).If there was an instrument which brought out both a passive guard (typically associated with a LO terminal)andan active driven guard (typically associated with HI terminals) to individually labelled terminals,how would you expect those terminals to be labelled?As the question implies, I'm interested in yourexpectationof what the labels would be. I'm trying to pick labelling that would be understood by most people without further explanation (implicitly, people who already know what a guard terminal is).I've already got a thought of what I'd use, but I don't want to prejudice people's answers.

author: Paul Price
author_rank: Super Contributor
timestamp: June 13, 2017, 09:37:33 pm
content: An Active Guard should be labeled "Active Guard", an inactive guard should be labeled Shield.

author: Someone
author_rank: Super Contributor
timestamp: June 14, 2017, 01:36:51 am
content: Right from the horses mouth:

author: Cerebus
author_rank: Super Contributor
timestamp: June 14, 2017, 02:07:53 pm
content: Still listening. I'm forgoing commenting for the time being; as I said, I don't want to inject my bias, just hear other people's expectations.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: June 14, 2017, 02:56:01 pm
content: Perhaps this may serve as an example:http://www.keysight.com/en/pd-4329A%3Aepsg%3Apro-pn-4329A/hr-meter?pm=PL&nid=-536900197.536897591&cc=US&lc=engHere is the manual:http://www.keysight.com/main/redirector.jspx?action=ref&cname=EDITORIAL&ckey=812048&lc=eng&cc=US&nfr=-536900197.536897591.00Several sections discuss when to connect GUARD to GND based on the type of measurement. It seems to be allowing for the configuration of a Passive Guard when strapped to GND, and an Active Guard when the low-impedance UNKNOWN is strapped to GND instead.

author: Cerebus
author_rank: Super Contributor
timestamp: June 14, 2017, 05:45:31 pm
content: Quote from: Tomorokoshi on June 14, 2017, 02:56:01 pmAs I think I made clear, I'm interested inpeople's expectations- what they will immediately comprehend by a particular label. There would be little point in asking around if I could get what I want from a search of the literature/manuals - I'm neither too stupid nor too lazy to be capable of that. Neither am I looking for tutorial on how to use a guard terminal.Again,I'm looking to find how I ought to label guard terminals when both active and passive guards are available so that the majority of people will understand what terminal represents what guardand to that end I'm interested inpeople's expectationsas to what those labels should be, not HP's standards, nor Keithley's, nor anybody else's standards.Weird isn't it, when you ask for facts on here, more often than not, you get a good helping of unsolicited opinion instead - often from the usual suspects(you know who you are). Here I am explicitly asking for personal opinions and people are trying to point me at facts instead.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: June 14, 2017, 06:53:01 pm
content: I'm sorry I couldn't meetyour expectations.My expectationis that it should be similar to how other equipment is labeled, backed up with instruction manuals for that equipment describes the function and use of those features.The point being was that particular piece of equipment had a fairly complex set of instructions for the unit, along with labeling on the terminals,due to the fact that it was not intuitively obvious of how it should be configured across the multiple measurement modes.You get what you pay for. What do you expect when you aren't upfront with this mysterious nomenclature you've invented?QuotePerhaps the problem isn't with the replies...

author: Cerebus
author_rank: Super Contributor
timestamp: June 14, 2017, 07:08:26 pm
content: Quote from: Tomorokoshi on June 14, 2017, 06:53:01 pmDon't get shirty, I just thought that perhaps I hadn't managed to explain myself clearly enough. Experience on here tells me that a goodly proportion of people skim, rather than read, questions; so it's good to be as explicitly clear about what you're asking for as possible. It also tells me that there are a lot of non-native English speakers, and they deserve as clear and unambigious explanation as possible as compensation for English being the price of admission.