Bips and Bops

Lesson 1.3

First week on the job. You're riding with your mentor, trying to absorb everything, trying not to look lost. He's talking about a controller he needs to check out and he says, casually, "Pull up the bips and bops on that thing." You look at him. He looks at you. He is not smiling. He is not joking. BIP: Binary Input Point. BOP: Binary Output Point. Welcome to building automation, where the terminology was apparently designed by people who never had to explain it to anyone.

Binary vs. Analog

Binary means two states. On or off. Open or closed. Energized or de-energized. There is no middle ground. A flow switch is either proving airflow or it isn't. When the controller reads a binary input it gets one bit of information: yes or no.

Analog is the opposite. An analog signal exists on a range; it's not yes or no, it's "how much." A temperature sensor doesn't say hot or cold. It says 72.4 degrees F. A pressure sensor says 1.43 inches of water column. The controller reads a voltage, a resistance, or a current value from the sensor and converts it into a number with engineering units.

Every manufacturer in this industry decided to name these things differently. Trane calls them BIPs and BOPs. Johnson Controls says BI and BO. Distech says DI and DO: digital in, digital out. Some platforms say AI for analog input, some say AIP.

The good news: once you understand what a binary input actually does, it doesn't matter what anyone calls it.

The Eight Point Types

Binary Input (BI, BIP, DI, SI, Contact): Reads an on/off signal from a field device. The circuit is either closed or open. Most binary inputs read dry contacts.

Binary Output (BO, BOP, DO, Relay Out): Switches a circuit on or off. Usually drives a relay. Key concept: dry vs wet relay outputs. A dry output is just a switch; you bring the power source. A wet output supplies voltage through the terminal.

Analog Input (AI, AIP, AIN): Reads a variable signal and converts it to an engineering unit. The sensor type determines what the controller expects: thermistor, 4-20mA transmitter, or 0-10V sensor.

Analog Output (AO, AOP, CMD): Sends a variable signal to control position or speed. The most common type is 0-10VDC.

Universal Input (UI): Flexible input, configured as analog or binary in software.

Configurable Output (CO): Flexible output, configured as analog or binary in software.

Universal Output (UO): Same concept as CO, different vendor name.

Software Points (AV, BV, Value, Variable, Setpoint): Exists only in the program. No physical terminal. No wire. Values the controller creates through calculation, logic, or scheduling.

Before you wire: check the jumpers: Many controllers use hardware jumpers on the board to configure how a terminal behaves. These are physical jumpers, not software settings, and the wrong position will make the point read garbage even if everything in the program looks correct.

How to Think About It

When you walk up to an unfamiliar controller, the first thing you do is find the I/O list. Once you know the point types, you know what to expect from every terminal on the board. Binary input? You're looking for a dry contact. Analog output? You're expecting a 0-10V signal going to an actuator.

Software points are where a lot of newer technicians get lost. They expect every value in the controller to have a wire behind it. It doesn't. Half of what a controller "knows" it calculated itself. Understanding the difference between a physical point and a software point is the difference between troubleshooting with a meter and troubleshooting with your brain. You need both.