Today, the interviewer asked a question that left me a bit confused
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I had an interview for a instrumentation engineer today, and the interviewer asked several questions. There was one question that I still don’t understand: it concerned the installation method of differential pressure gauges, with an L side and an H side. I said that H should be installed at the bottom and L at the top. He then asked what if the pressure at the bottom is -100 and the pressure at the top is -50. I said that such a situation shouldn’t occur, but he said it does, and since he thought I didn’t understand, he stopped asking questions. I want to know where I went wrong – does such a situation really exist? Please ask an expert to explain it
Pressure at the top: -50, pressure at the bottom: -100; these are the pressures at the two pressure sampling points inside the container
I’m a bit puzzled by what you said. First of all, as an instrumentation engineer, if you don’t clarify the process details, you might fall for it; just because he mentioned a differential pressure gauge? Is it a pressure gauge? Are you still talking about the pressure transmitter? Maybe when he spoke, you thought he was referring to measuring the liquid level. But then he said that the pressure below is -100 and the pressure above is -50. Do you think such a situation doesn’t exist? What if it’s a pipe? For example, in the case of a flue gas flow from top to bottom, it could be the situation he is referring to. But your unit didn’t specify clearly –100 pa? If it’s -100 KPa, that seems to not exist on Earth
He was referring to a container, which is obviously used as a level gauge; the unit should be kPa. I didn’t ask in detail. Since it’s an interview, I think asking general questions is enough to gauge the other person’s competence – there’s no need to ask such tricky questions. But you’re right, it’s possible that it’s related to flues; in that case, it would be considered a Venturi tube
H for the high-voltage side, L for the low-voltage side – this is definitely the correct answer; it’s not appropriate to use up and down as a distinction
Firstly, on the Brady and other differential pressure gauges, there are no H or L indicators at all; on-site, assistance from others is still required for making judgments. Also, when the interviewer speaks, don’t rush to respond—there are traps in what they say. Last time, someone asked me a question about explosion-proof areas; the client insisted that instruments in non-explosion-proof areas also need to be of DIICT6 grade. I said I had sent an email reminding the client that this was not necessary. The interview still wasn’t satisfied with the answers. It’s also possible that the company simply doesn’t want to hire anyone
The question refers to pressure vessels, without mentioning the measurement of liquid level within them. It could be a gas pressure vessel, with air intake at the top and suction at the bottom; in that case, the pressure might be -50 kPa at the top and -100 kPa at the bottom.