Which of the following is NOT a standard to transmit measurement and control signals?
Show Hint
- 4 – 20 mA
- 3 – 15 psig
- 0 – 100%
- 1 – 5 VDC
The Correct Option is C
Solution and Explanation
4–20 mA (electrical current),
3–15 psig (pneumatic signal), and
1–5 VDC (voltage signal).
However, 0–100% is only a representation of process output (like controller output), not an industry-standard transmission signal.
Therefore, (C) is the correct answer.
Top Questions on Measurement of process variables
- Consider the surge drum in the figure. Initially, the system is at steady state with a hold-up \( V = 5 \) m³, which is 50% of the full tank capacity, \( V_{\text{full}} \), and volumetric flow rates \( \vec{F}_{\text{in}} = \vec{F}_{\text{out}} = 1 \) m³/h. The high hold-up alarm limit \( V_{\text{high}} = 0.8 V_{\text{full}} \) while the low hold-up alarm limit \( V_{\text{low}} = 0.2 V_{\text{full}} \). A proportional (P-only) controller manipulates the outflow to regulate the hold-up \( V \) as \( \vec{F}_{\text{out}} = K_c (V - \vec{V}) + \vec{F}_{\text{out}} \). At \( t = 0 \), \( \vec{F}_{\text{in}} \) increases as a step from 1 m³/h to 2 m³/h. Assume linear control valves and instantaneous valve dynamics. Let \( K_c^{\text{min}} \) be the minimum controller gain that ensures \( V \) never exceeds \( V_{\text{high}} \). The value of \( K_c^{\text{min}} \), in h\(^{-1}\), rounded off to 2 decimal places, is _____.
- GATE CH - 2024
- Instrumentation and Process Control
- Measurement of process variables
- A PD controller with transfer function \( G_c \) is used to stabilize an open-loop unstable process with transfer function \( G_p \), where \( G_c = K_c \frac{(T_D s + 1)}{(\frac{T_D}{20})s + 1} \) and \( G_p = \frac{1}{(s - 1)(10s + 1)} \), and time is in minutes. From the necessary conditions for closed-loop stability, the maximum feasible value of \( T_D \), in minutes, rounded off to 1 decimal place, is _____.
- GATE CH - 2024
- Instrumentation and Process Control
- Measurement of process variables
- Consider the block diagram in the figure with control input u, disturbance d and output y. For the feedforward controller, the ordered pair (K, a/ẞ) is
- GATE CH - 2024
- Instrumentation and Process Control
- Measurement of process variables
Choose the option that correctly pairs the given measurement devices with the quantities they measure.
\[ \begin{array}{c c c c} \underline{S\ No} & \underline{\text{Measurement Device}} & \underline{S\ No} & \underline{\text{Measured Quantity}} \\ \text{I} & \text{Bourdon Gauge} & \text{A} & \text{Temperature} \\ \text{II} & \text{Orifice Plate meter} & \text{B} & \text{Concentration} \\ \text{III} & \text{Pyrometer} & \text{C} & \text{Pressure} \\ \text{IV} & \text{Colorimeter} & \text{D} & \text{Flow rate} \\ \text{V} & \text{Pirani Gauge} & \text{E} & \text{Liquid level} \\ \end{array} \]- GATE CH - 2022
- Instrumentation and Process Control
- Measurement of process variables
Questions Asked in GATE CH exam
Consider a process with transfer function: \[ G_p = \frac{2e^{-s}}{(5s + 1)^2} \] A first-order plus dead time (FOPDT) model is to be fitted to the unit step process reaction curve (PRC) by applying the maximum slope method. Let \( \tau_m \) and \( \theta_m \) denote the time constant and dead time, respectively, of the fitted FOPDT model. The value of \( \frac{\tau_m}{\theta_m} \) is __________ (rounded off to 2 decimal places).
Given: For \( G = \frac{1}{(\tau s + 1)^2} \), the unit step output response is: \[ y(t) = 1 - \left(1 + \frac{t}{\tau}\right)e^{-t/\tau} \] The first and second derivatives of \( y(t) \) are: \[ \frac{dy(t)}{dt} = \frac{t}{\tau^2} e^{-t/\tau} \] \[ \frac{d^2y(t)}{dt^2} = \frac{1}{\tau^2} \left(1 - \frac{t}{\tau}\right) e^{-t/\tau} \]- GATE CH - 2025
- Process Control
Choose the transfer function that best fits the output response to a unit step input change shown in the figure:
- GATE CH - 2025
- Control Systems
- Rohit goes to a restaurant for lunch at about 1 PM. When he enters the restaurant, he notices that the hour and minute hands on the wall clock are exactly coinciding. After about an hour, when he leaves the restaurant, he notices that the clock hands are again exactly coinciding. How much time (in minutes) did Rohit spend at the restaurant?
An electrical wire of 2 mm diameter and 5 m length is insulated with a plastic layer of thickness 2 mm and thermal conductivity \( k = 0.1 \) W/(m·K). It is exposed to ambient air at 30°C. For a current of 5 A, the potential drop across the wire is 2 V. The air-side heat transfer coefficient is 20 W/(m²·K). Neglecting the thermal resistance of the wire, the steady-state temperature at the wire-insulation interface __________°C (rounded off to 1 decimal place).
GIVEN:
Kinematic viscosity: \( \nu = 1.0 \times 10^{-6} \, {m}^2/{s} \)
Prandtl number: \( {Pr} = 7.01 \)
Velocity boundary layer thickness: \[ \delta_H = \frac{4.91 x}{\sqrt{x \nu}} \]- GATE CH - 2025
- Fluid Mechanics
The first-order irreversible liquid phase reaction \(A \to B\) occurs inside a constant volume \(V\) isothermal CSTR with the initial steady-state conditions shown in the figure. The gain, in kmol/m³·h, of the transfer function relating the reactor effluent \(A\) concentration \(c_A\) to the inlet flow rate \(F\) is:
- GATE CH - 2025
- Fluid Mechanics