1. Connection between Siemens 1200 and incremental encoder
The Siemens 1200's digital input switches all provide a fast counter function for the incremental encoder pulse signal, reaching 200kHz for single-phase signals and 80kHz for two-phase signals (with frequency quadrupling and direction determination capabilities). For the commonly used 2500 PPR (pulses per revolution), the fastest speed reaches 1920 RPM (revolutions per minute). The incremental encoder signal is a PNP unidirectional open-circuit signal. It is recommended to select a 10-30V push-pull output type incremental encoder, such as the GI58N incremental encoder.
2. Connection of Siemens 1200 with 4-20mA signal of absolute encoder
Absolute encoder signals are not susceptible to interference, and data is not lost during power outages. PLCs do not need to constantly count absolute encoders, and CPU scanning does not require calculating interruption times, thus saving CPU resources. In particular, the market price of absolute encoders has dropped significantly, and due to the improved data reliability, using absolute encoders can save debugging time and reduce after-sales service costs. The actual performance and cost-effectiveness are far superior to those of incremental encoders. More and more users are choosing absolute encoders for PLC positioning.
Due to the economic efficiency of the Siemens 1200, the preferred connection method for absolute encoders is the 4-20mA signal interface, which is more economical and convenient. The Siemens 1200 comes with two 4-20mA input interfaces, which can be directly connected to two absolute encoders with 4-20mA output interfaces.
Absolute encoders are divided into single-turn absolute encoders and multi-turn absolute encoders. A single-turn absolute encoder refers to an encoder that operates within a 360-degree range or between 0 and 180 degrees. For this type of encoder, 4mA corresponds to 0 degrees, and 360 degrees (or 180 degrees) corresponds to 20mA. The data in the PLC linearly corresponds to the angle value; each value corresponds to a unique angle. This data does not require counting, is unaffected by interference or power outages, and can be directly programmed. The recommended single-turn absolute encoder is the GMS412.LB (code 9400S) . This encoder allows setting the angle value, rotation direction, and zero-point offset corresponding to 20mA. For example, 20mA can be set to correspond to 180 degrees, allowing the encoder to operate within the 0-180 degree range.
In PLC positioning control for length or height, encoders often need to rotate more than 360 degrees within a working range, requiring the selection of multi-turn absolute encoders. Multi-turn absolute encoders with 4-20mA outputs come in two types: one is a fixed-range multi-turn absolute encoder, such as 16 turns, 64 turns, or 256 turns, where 20mA corresponds to the end of 16 turns, 64 turns, or 256 turns. This type of encoder is more economical, and the recommended model is GEX60.LB . The other type is an intelligent multi-turn absolute encoder, where the 20mA can be set at any position between 1 and 4096 turns, and a zero-point offset can be set. The recommended model is GAX60.LB (code 9600) . This encoder has extremely wide applications and has been successfully used in many fields such as hoisting, water conservancy, military, petroleum, chemical, and various industrial machinery.
3. Connection of Siemens 1200 with absolute encoder RS485 or Modbus RTU signals
The Siemens 1200 is configurable with an RS485 communication interface, which can connect to RS485 signals from absolute encoders, including single-turn and multi-turn absolute encoders. There are various forms of RS485 signals for absolute encoders, the most common being the simple RS485 broadcast mode (master mode, active broadcast transmission), the free protocol with address-based command transmission (slave mode), and Modbus RTU mode. If only one absolute encoder is connected, the encoder active mode can be used, as it offers a simple protocol and reliable signal. However, if multiple encoders need to be connected (bus mode), the Modbus RTU mode can be selected. But because this mode requires polling, the data refresh from each encoder is slow, making it unsuitable for controlling fast-moving devices.
Recommended active mode RS485 encoders: single-turn absolute value models are GES38 . RDB, GES60 . RDB, or GMS412 . LB (code 9400S); multi-turn absolute value models are GEX60 . LB (64 turns) or GAX60 . LB (code 9600) (4096 turns).
The recommended passive command mode RS485 encoder (can connect 1-9 encoders, including address) is the single-turn absolute value model GMS412 . LB (code 9400S); the multi-turn absolute value model is GEX60 . LB (64 turns) or GAX60 . LB (code 9600) (4096 turns).
The recommended encoders for Modbus RTU mode are GMS412 ( RMB) for single-turn absolute values and GAX60 (RMB ) (4096 turns) for multi-turn absolute values.
4. Connection of Siemens 1200 with Profibus-DP signal of absolute encoder
The Siemens 1200 can be configured with a Profibus-DP bus communication interface, which is the most commonly used output mode for European absolute encoders. Various imported European brand encoders, including domestic brands, can be selected. This interface is commonly used by Siemens, but encoders with this interface are expensive, including the cost of configuring cables and wiring. It is no longer economical for the 1200 and is not recommended here.
5. Practical Case: Connecting a Siemens 1200 encoder to a 4-20mA absolute encoder for simple positioning control.
Practical Application Introduction 1: Single-machine and multi-machine control of water gate height. The lifting height of flood control, water storage, water supply, and sewage gates across the country is controlled by winch cranes (gate hoists). Each gate station has 1-6 gate hoists. A Siemens 1200 PLC connected to a 4-20mA interface of an absolute multi-turn encoder, configured with an HMI, can effectively perform this simple positioning control. The encoder can be installed on the winch drum shaft or the reduction gear shaft. The required number of encoder rotations is pre-calculated, and the encoder output 20mA is set greater than this number, for example, 16 rotations. Thus, every 1mA change in the encoder output 4-20mA linearly corresponds to one rotation of the drum. This is used to calculate the change in gate lifting height to control the opening and closing height of the water gate. The selected encoder model is the recommended GAX60.LB (code 9600). Project application locations: multiple water gates in Harbin, Northeast China, and Changzhou, Jiangsu Province.
Practical Application Introduction 2: Hydraulic Dual Cylinder Lifting Synchronous Control. Larger sluice gates require the use of two hydraulic cylinders on the left and right sides for power lifting, maintaining synchronized positions to ensure smooth lifting and lowering of the gate. A sluice gate in Guangdong originally used a gate opening gauge for display purposes. However, the original gauge had low reliability and could not perform synchronous correction and lifting control of the hydraulic cylinders. The user wanted to replace the original gauge with a small, economical PLC with an HMI to improve control reliability and programmability. A Siemens 1200 PLC was selected, along with two absolute multi-turn encoders with 4-20mA signal interfaces: two GAX60 LB (code 9600) . These were mechanically installed to correspond to the lifting heights of the left and right cylinders, with a corresponding cylinder height of 6 meters and a 20mA input. The two 4-20mA signals were connected to the analog input interface of the 1200 PLC. The PLC compared two sets of data and controlled the solenoid valves of the hydraulic systems of the left and right cylinders based on the height difference, adjusting the flow rate of the hydraulic oil circuits to regulate the lifting or lowering speed and position difference of the cylinders, maintaining synchronous correction and lifting control of the two cylinders. The Siemens 1200 PLC is equipped with two absolute encoders with 4-20mA interfaces, which perfectly accomplishes such synchronous correction and lifting control.
