EETC Instrumentation 3

Question 1

Which type of pressure measurement compares process pressure to atmospheric pressure?

Accepted Answer

Gauge pressure

Answer

Gauge pressure (psig) uses atmospheric pressure (14.696 psia at sea level) as its reference, so a reading of 0 psig equals atmospheric.

Question 2

A pH sensor outputs approximately how many millivolts per pH unit at 25°C?

Accepted Answer

59.16 mV/pH

Answer

The Nernst equation predicts approximately 59.16mV/pH unit response for a glass electrode at 25°C (298K).

Question 3

An orifice plate in a pipeline causes flow measurement errors when:

Accepted Answer

The upstream straight pipe run is too short

Answer

Insufficient straight pipe upstream causes turbulent or asymmetric velocity profiles that deviate from the conditions assumed in the orifice calibration.

Question 4

In a HART (Highway Addressable Remote Transducer) system, digital communication is superimposed on the 4-20mA signal using:

Accepted Answer

FSK at 1200 baud over the analog loop

Answer

HART uses Bell 202 FSK (Frequency Shift Keying) — 1200Hz for logic '1' and 2200Hz for logic '0' — overlaid on the DC 4-20mA signal without disrupting it.

Question 5

What is the purpose of a cold junction compensation circuit in a thermocouple instrument?

Accepted Answer

To correct for the ambient temperature at the reference junction

Answer

Cold junction compensation measures the terminal block temperature and adds the equivalent voltage so the instrument reads true process temperature regardless of ambient conditions.

(EETC) Electrical Technician Certification Practice Test

(EETC) Electrical Technician Certification Practice Test

EETC Instrumentation 3