Caledon Controls - What's New

This page shows details of products which will be introduced in the near future. Please contact us for latest details of release dates or more information

Index
STC3000 Thyristor Stacks	New Instrumentation Products
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Download User Manual (.pdf)

STC3000 THREE PHASE THYRISTOR STACKS

GENERAL DESCRIPTION

This is a modern range of thyristor stacks, specifically designed for control of AC heating loads in medium and high current applications for furnaces, ovens, dryers etc. These stacks are particularly useful where current limit is required (eg loads with low cold resistance), or for use with generator sets, or when feeding the primary of transformers. They are fitted with 2 analogue inputs and one analogue output, 6 isolated digital inputs, and 2 isolated digital outputs, 1 relay alarm output, and Modbus ^® RTU compatible comms, providing a comprehensive systems capability. DeviceNet or Profibus DP communications are available as an option.

OVERVIEW OF FACILITIES

The stacks operate in either phase angle mode, or soft start burst fire mode. Provision is made to switch between operating modes using a digital input. Current limit may be applied in either mode; in burst fire mode the stack will phase back if current limiting action is required. In burst fire mode the cycle time and the soft start / finish times may be independently set.

In phase angle mode the stack may either be operated open loop, or closed loop with V, I, V², I², V rms x Irms, or I² / V² transfer feedback. The I² / V² transfer is useful with loads which have a low cold resistance. The control signal initially controls the current fed to the load, until the voltage feedback signal becomes greater than the current feedback signal, when control is switched to voltage. Current limit action may also be applied.

In burst fire mode the stack operates open loop, with or without line voltage feedforward compensation, as selected.

Control and limit setpoints may be provided as analogue inputs, settings on the LCD display, or via the comms link. There are two analogue inputs, so one may be assigned to control and one to a limit setpoint.

Setpoints available are; control, current limit, voltage limit, power limit. In theory all can be operational simultaneously.

Provision is made for limit setpoints to be activated / de-activated by means of digital inputs.

Six opto-isolated digital inputs are provided. These may be used as either sink or source in association with 24V DC plc / logic systems, or, using the energising supply provided, with volt free contacts.

They are assigned to; phase angle / burst fire select; 3 off limit enable; control setpoint local (keypad or comms) / remote; stack enable.

Two opto-isolated digital outputs are provided, which may be used as either sink or source in conjunction with 24V DC plc or relay logic.

They are used to indicate that the stack is enabled and whether a limit setpoint is controlling the load current or voltage.

In addition a relay output is available (volt free contacts), contacts rated up to 250V AC, which is allocated to an alarm condition.

One analogue output is provided, which may be used as a retransmission signal of; Load Voltage, Load current (average of 3 currents), Load Power.

NEW INSTRUMENTS

The following instruments are all designed in the form of DIN rail mounting modules (similar to the Current and Voltage Monitor), and require a 24V DC power supply, or optional 115 / 230V supply. Optional Modbus communications are also available on some instruments.

BURST FIRE THYRISTOR / SOLID STATE RELAY DRIVER

This instrument accepts an analogue input signal (0-5V, 0-10V, 1-5V, 0-20mA, 4-20mA) and provides logic firing pulses to drive a solid state relay or thyristor in burst fire mode.

ADVANCED SINGLE CYCLE THYRISTOR / SOLID STATE RELAY DRIVER

This instrument accepts an analogue input signal from a temperature controller, and provides 3 logic signal outputs to drive solid state relays or thyristor stacks in a 3-phase (4-wire) load configuration. The load power is controlled in single cycle mode, in which 50% power is delivered by switching alternate cycles, below 50% power is controlled by switching 1 cycle on followed by a number of cycles off, and above 50% power is controlled by switching 1 cycle off and a number of cycles on. This control technique minimises flicker and load temperature cycling, and is particularly suitable for use with fast infrared heaters and silicon carbide (Crucilite) heater elements. A microprocessor is used in this instrument to generate trains of cycles which accurately average the required load power, and enables this mode of control to be implemented with low cost solid state relays and logic input thyristor stacks.

STAGING CONTROLLERS

Staging controllers accept a single analogue input from a PID temperature controller, and provide multiple outputs to control the total power delivered to the load by means of a number of power sources each of which is rated at a lower power output than the total load requirement. This is sometimes achieved, for example, by switching in heater banks at different setpoints as the temperature falls, but this technique inevitably results in a fall in temperature as the the load demand increases. The staging controller makes full use of the PID temperature controller to eliminate this 'temperature droop'.