BACKGROUND

Most servo/stepper drives and motion controllers have a provision for limit sensors, which are used to prevent a load from traveling beyond the end of an actuator. Home sensors are used to provide a reference on the machine for establishing a zero position. Limit and home sensors (as well as some other digital sensors) come in two main electrical configurations: NPN and PNP.

To prevent confusion, we need to define three sets of terms that are often confused:

• NPN and PNP

• Sinking and Sourcing

• Normally Open and Normally Closed

NPN AND PNP

These terms actually refer to types of transistors. Without getting into details, an NPN transistor turns on when bias current flows from the base (the transistor's control terminal) to the emitter. This means base voltage must be higher at the base than at the emitter.

Conversely, a PNP transistor turns on when bias current flows from the emitter to the base. The base voltage must be lower than the emitter voltage.

What this means from a practical standpoint is that to turn on an NPN transistor, you connect the base to a voltage source. To turn on a PNP transistor, you ground the base.

SINKING AND SOURCING

These terms are a bit more straightforward. A sinking sensor is one that sinks current to ground when it turns on. A sourcing sensor is one that provides current from a voltage source when it turns on.

These terms apply to more than just sensors. Digital inputs and outputs can also be described as sinking or sourcing. The important thing to understand is that a sinking sensor must be connected to a sourcing input and a sourcing sensor must be connected to a sinking input.

NORMALLY OPEN AND NORMALLY CLOSED

A normally open sensor is one that is open (non-conducting) most of the time. It closes (conducts) when it is activated. A momentary pushbutton is an example of a normally open circuit.

A normally closed sensor is one that is closed (conducting) most of the time. It opens (stops conducting), when it is activated. An emergency stop button is an example of a normally closed circuit.

It is important to note that normally open/closed has nothing to do with NPN/PNP or sinking/sourcing. You can get NPN/PNP and sinking/sourcing sensors in both normally open and normally closed configurations.

HOW NPN/PNP AND SINKING/SOURCING RELATE

Due to their electrical characteristics, NPN and PNP transistors generally work best in specific uses. NPN transistors are well-suited to sinking applications and PNP transistors are best used for sourcing ones.

Because of this, common practice is to use the terms "sinking" and "NPN" interchangeably when talking about sensors and switches. Sourcing and PNP are the same way.

TLDR: NPN sensors are sinking sensors and must be connected to sourcing inputs. PNP sensors are sourcing sensors and must be connected to sinking inputs.

DRIVE COMPATIBILITY

Some Parker drives are compatible with NPN sensors, some with PNP and some with both. The table below summarizes.

ACTUATOR OPTION COMPATIBILITY

Parker actuators usually have multiple limit/home sensor configurations available. It is important to choose one that is compatible with your servo drive. The tables below show each actuator series with recommended limit/home codes listed for NPN and PNP. The tables also show the limit switch part numbers in case replacements ever need to be ordered. If the previous table shows your drive/controller is compatible with NPN, make sure to choose an NPN option from the table below.

NOTE: The mSR080 and mSR100 have NPN limit switches built in. If encoder option M1 (magnetic µm) is used on the mSR100, then the stage is provided with a normally open NPN home sensor. For option R1 (50 nm BiSS-C) is used on the mSR100, there is no home switch. All other encoder options for the mSR080 and mSR100 have an encoder Z channel instead of a home switch. This goes to the encoder input.

What if you already have an actuator and it doesn't have one of the options listed above? Can it still work with your Parker drive? Very often the answer is yes. The table above is a good quick reference for new applications, but does not show every compatible option. Refer to the product documentation for descriptions of each limit option and evaluate them for compatibility based on whether they are NPN or PNP.

SPECIFICATIONS AND DIAGRAMS

P8SA SENSORS

PART NUMBERS

DIMENSIONS

WIRING

400XR SENSORS

PART NUMBERS

DIMENSIONS

WIRING

The flying-lead sensors for the XR series ship with four wires and can be connected as either normally open or normally closed.

The sensors that come with M8 connectors for the XR have three wires.

HPLA SENSORS

PART NUMBERS

DIMENSIONS

WIRING

MSR SENSORS

PART NUMBERS

Spare sensors are not available for the mSR because they are built into the encoder readhead. If a sensor fails, the unit needs to be returned to Parker for repair.

WIRING

The mSR is typically used in conjunction with a breakout cable that converts its two D-sub connectors into connectors and leads compatible with Parker drives. Refer to those cable prints for wiring information:

• 006-2690-01 (IPA)

• 006-2691-01 (P Series)

Customers needing to build their own cable sets (e.g. for third-party drives) should refer to the product documentation:

• mSR100 Miniature Positioners - User Guide

• mSR100 Miniature Positioners - User Guide

EXTENSION CABLES

These cables terminate in flying leads and are compatible with all Parker limit/home switches that have an M8 connector. Wire colors are brown (+), blue (-) and black (sense) just like the limit switches.

PARKER NUMBERS

QUICK LINKS

[Related FAQ: P8S Position Sensor Order Codes]