Field Devices and VFDs

Learning objectives

• >Identify common BAS sensors and their signal types (4–20 mA, 0–10 V, RTD/thermistor, dry contact)
• >Classify any point as AI, AO, BI, BO or a network point
• >Explain valve authority and how pressure-independent control valves (PICVs) change system behavior
• >Compare hardwired and networked VFD integration

Sessions

Three 2-hour weeknight sessions plus a weekend block. Check each one off as you finish it.

1. SESSION 1· 2 h Honeywell manual: sensors and signal types (4–20 mA, 0–10 V, RTD/thermistor, dry contact)
2. SESSION 2· 2 h Belimo University videos on valves, valve authority, pressure-independent valves and actuators
3. SESSION 3· 2 h A Danfoss Drives webinar on BAS integration (hardwired vs network control)
4. WEEKEND· 2 h Exercise: a full points list for a VAV air handler or a chilled-water pump set, with every point classified

Answer in your notebook first, then reveal the answer and grade yourself honestly.

1. Q1Give two advantages of a 4–20 mA signal over 0–10 V on a long wire run.

   [ reveal answer ]

   It isn't affected by voltage drop or much electrical noise. Its live zero (4 mA) also reveals a broken wire.

   ✓ I got it ✗ Missed it

2. Q2Classify each point: pump status from a current switch, VFD speed command, DP sensor, pump start/stop.

   [ reveal answer ]

   BI, AO, AI, BO.

   ✓ I got it ✗ Missed it

3. Q3What is valve authority, and roughly what value do designers aim for?

   [ reveal answer ]

   The valve's pressure drop divided by the total branch pressure drop. Designers typically aim for about 0.5, and at least 0.25.

   ✓ I got it ✗ Missed it

4. Q4How do PICVs affect the choice of DP setpoint for a variable-speed pump?

   [ reveal answer ]

   PICVs hold flow regardless of pressure changes within their range, so the DP setpoint only needs to cover the PICV minimum plus the branch losses. That allows a lower setpoint and makes balancing simpler.

   ✓ I got it ✗ Missed it

5. Q5Name two data points a networked VFD provides that a basic hardwired connection does not.

   [ reveal answer ]

   Any two of: kW, kWh, motor current, fault and warning codes, run hours, DC bus voltage.

   ✓ I got it ✗ Missed it