1. Ordering Codes

Ordering Codes

PCM-1B

Power Control Module

Single Phase

Burst (Time Proportioned) Drive

2. Description

The PCM-1B is a Zero Cross Time Proportioned Power Control Driver Board designed for use with high power back to back SCR modules driving resistive loads. The power delivered to the load is proportional to the command input signal. The gate drive technique used in the PCM-1B is DC drive for the reliable firing.

Features:

• True DC SCR Gate Drive
• Time Proportioning/Burst Firing
• Zero Cross Firing for Low EMI
• High Resolution Fast Synchronous Burst Output
• Suitable for resistive Loads
• 4-20mA, 0-10V, 0-5V, Pot, PWM Inputs
• 50/60Hz and 100 – 265VAC operation
• Adjustable Power limit
• LED power, output and limit indicators

3. Installation / Safety Information

Responsibility for determining suitability for use in any application / equipment lies solely on the purchaser, OEM and end user. Suitability for use in your application is determined by applicable standards such as UL, cUL and CE and the completed system involving this component should be tested to those standards.

[warning] WARNING: FIRE HAZARD!! Even quality electronic components CAN FAIL KEEPING FULL POWER ON! Provide a SEPARATE (redundant) OVER TEMPERATURE SHUTDOWN DEVICE to switch the power off if safe temperatures are exceeded.

[warning] WARNING: HIGH VOLTAGE!! This control board has high voltage on it that can cause death. This control must be installed in a GROUNDED enclosure by a qualified electrician in accordance with applicable local and national codes including NEC and other applicable codes. Provide a safety interlock on the door to remove power before gaining access to the device.

3.1 Mounting Instructions

The PCM-1B mounts using four #6 screws. See the mechanical dimensions section for more details. The PCB should be mounted at least 0.500" from any surface.

3.2 Electrical Connections

See the WIRING DIAGRAMS at the end of this document. Make sure the unit ordered is the correct unit for the application before wiring. Before wiring the unit, all Dip Switch settings for the command input and special features should be setup properly per the Dipswitch Configuration Section.

3.3 SCR Output Snubbers and Transient Protection

3.3.1 Commutation Problems

When an SCR or TRIAC is used to control an inductive load, the load current lags the mains voltage. When the device turns off at zero current, the rate of rise of the reapplied voltage can retrigger the device and produce half cycling and blown fuses. To limit this rate of rise and obtain reliable commutation, an R-C (resistor-capacitor) snubber circuit should be connected in parallel with the SCR/TRIAC.

3.3.2 dv/dt Problems

When voltage transients occur on the mains supply or load of an SCR/TRIAC it can cause the device to turn on unexpectedly due to the fast rate of rise of voltage (dv/dt). This can result in false firing and half cycling of the load that can cause blown fuses when driving inductive loads. An R-C snubber circuit will help to limit the dv/dt seen by the device and will produce more reliable firing.

3.3.3 Snubber Sizing

When an SCR using an R-C snubber turns on, the capacitor is discharged through the resistor into the device resulting in high peak currents. It is critically important when sizing your snubber to make sure that the resistor value does not become so low that the ratings of the SCR are exceeded when the capacitor is discharged. Careful attention should also be given to the power dissipation that will develop in the snubber resistor.

3.3.4 MOV Protection

Metal Oxide Varistors are used on SCRs to suppress voltage spikes that can occur across the devices and damage them. Snubbers are not a substitute for MOVs and vice versa. Snubbers and MOVs should be used together to get reliable performance and long life from the SCR/TRIAC application. External MOV must be installed across SCRs to limit peak voltages seen by the PCM-1B to ~800VDC.

3.4 Limited Warranty

NuWave Technologies, Inc. warrant this product to be free from defect in workmanship and materials for a period of one (1) year from the date of purchase.

1. Should unit malfunction, return it to the factory. If defective it will be repaired or replaced at no charge.
2. There are no user serviceable parts on this unit. This warranty is void if the unit shows evidence of being tampered with or subjected to excessive heat, moisture, corrosion or other misuse / misapplication.
3. Components which wear or damage with misuse are excluded, e.g. relays.
4. NuWave Technologies, Inc. shall not be responsible for any damage or losses however caused, which may be experienced as a result of the installation or use of this product. NuWave Technologies, Inc. liability for any breach of this agreement shall not exceed the purchase price paid E. & O.E.

4. Operation

4.1 Power Supply

The PCM-1B power supply requirement is 90-265VAC 47-63Hz. The line synchronization for the zero cross firing is derived from the power supply input.

4.2 Power Fusing

A 100mA user serviceable fuse is provided. Under normal circumstances this fuse should not open. If it opens, one of the following conditions may have caused it:

1. A large power line transient occurred.
2. The PCM-1B was wired incorrectly and excess voltage was applied.
3. The PCM-1B malfunctioned and requires service.

4.3 Command Input

The PCM-1B can accept 4-20mA, 0-20mA, 0-10V, 2-10V, 0-5V, 1-5V, Potentiometer and TTL PWM inputs. All analog commands are isolated from the power line and SCR drive outputs. The type of command input can be configured via the dipswitch. The default setting is 0-5V/potentiometer. Connecting the power to any part of the command input or SCR drive outputs will cause damage to the unit.

4.4 Cycle Times

The cycle time refers to the total time between an on and off cycle.

A line graph illustrating 'LOAD POWER' over 'TIME'. The graph shows a series of rectangular pulses representing the load power being switched on and off in cycles. An arrow indicates the 'CYCLE TIME' as the duration between the start of one on-period and the start of the next.

The PCM-1B has 4 available cycle times settable via the dipswitches. The cycle times are specified below in # of cycles and can be correlated to their respective times using the table below for both 50 and 60 Hz Line frequencies.

4.5 Cycle Times – 266mS Selection (Fast Synchronous Burst Firing)

*Synchronous Firing Method: When burst firing AC with conventional PWM, there is a tradeoff between resolution and cycle time. Generally the cycle time should be chosen based on the mass of the load to be controlled; the larger the load mass, the longer the cycle time can be. For the best possible resolution, it is standard practice to choose the longest cycle time that can be used without causing process ripple. Longer cycle times generally provide greater control resolution, but the Fast Synchronous Burst setting provides excellent resolution with a fast cycle time.

When the PCM-1B cycle time is set to 266mS (320mS @ 50Hz) the Fast Synchronous Burst Firing mode is turned on. The cycle time becomes longer near zero and full power levels to provide improved control resolution. For Example, since the PCM-1B generally modulates 16 AC cycles, the lower limit in power that will maintain the cycle time is 1/16 or 6.25%. The PCM-1B will use increased off periods below 6.25% power and above 94.75% power.

4.5.1 Fast Synchronous Burst Firing Mode

As shown below, the PCM-1B Fast Synchronous Burst Firing mode selectively fires fractional numbers of cycles. Since pulse width modulation alone would limit the resolution to 16 steps or 6.25% when modulating 16 AC cycles, a proprietary algorithm is employed to provide improved control resolution. In this firing mode, the cycle time is varied as well as the on time. To select the Fast Synchronous Burst Firing Mode set Diswitches 1 and 5 to the off position.

A series of waveform diagrams depicting the output power over time for different power levels using the Fast Synchronous Burst Firing mode. Each waveform shows AC cycles being switched. The diagrams illustrate how the number of AC cycles or the off-time varies to achieve different power outputs, from 25% to 100%.

4.5.2 Fast Synchronous Burst Firing Advantages

The two plots below are actual data for a 425 degF capable 10KW resistive heater ramped from 0-100% power over two hours. The first plot shows straight 16 cycle, 266mS cycle time PWM. Note the nonlinearity humps due to poor resolution. The second plot shows the linearity improvement with the Fast Synchronous Burst. Any visible overall curvature is a normal heater characteristic.

Two line graphs comparing power output over time. The top graph, labeled 'Fast PWM of zero cross fired loads can result in poor linearity / resolution', shows a stepped, less linear ramp-up. The bottom graph, labeled 'NuWave Fast Synchronous Burst algorithm results in excellent linearity / resolution', shows a smoother, more linear ramp-up, demonstrating improved control.

4.5.3 PWM Command Input

The PWM input is designed to accept a push-pull 5V/TTL level drive at a frequency of 1KHz-100KHz.

4.5.4 Input Fail-safe Protection

If the signal sent to the PCM-1B's command input becomes electrically open the control output will be forced to a low output power state.

4.1 Power Limit

This feature will clip the command signal to a level set by the on-board potentiometer. The Voltage Limit is adjustable from 0% to 100% of the max load voltage. When the PCM-1Bis actively holding back or “limiting” the command via voltage limit, the RED “LIMIT” LED will become energized.

Other combinations of primary and secondary turns ratios may be used as long as the 200mA RMS and 5V peak of the CT input are not exceeded.

4.2 Configuration Dipswitch

The configuration dipswitch is used for setting up the command input, line soft start and limit as follows:

4.3 Indicator LEDs

4.3.1 Power LED

The Green Power LED will illuminate when power is applied.

4.3.2 SCR Drive LEDs

The RED SCR Drive LEDs will turn on when the SCR drive output is on. If the SCR gate is not wired properly or not connected, the LED will not illuminate. The LED should only be used as a rough indication of SCR Drive and not actual power output.

4.3.3 Limit LED

The RED Current Limit LED will illuminate when the Power limit is actively limiting the command input.

5. Electrical Specifications

5.1 SCR Gate Drive Profile

A graph showing 'Gate current' on the Y-axis and 'Time' on the X-axis. It illustrates the SCR gate drive characteristics, showing a rapid rise time of approximately 200nS to a peak current of 1.6A, followed by a sustained current of 160mA throughout the conduction period. The pulse width is indicated as approximately 50uS.

5.2 Input Specifications

• Command Inputs: 4-20mA, 0-20mA, 0-10V, 2-10V, 0-5V, 1-5V, Pot, PWM
• Input Impedance: 10K Ω (0-10V), 250Ω (4-20mA), 100KΩ (0-5V)
• Response Time: <16mS (or Cycle Time Selection)
• PWM Input Frequency: 1KHz-100KHz
• PWM Input Level: 5 VDC TTL Level
• External Potentiometer Res.: 1KΩ-25KΩ
• Command to Mains Isolation: 2500Vrms
• Command to SCR Drive Isolation: 2500Vrms

5.3 Output Specifications

• Control Range: 0 – 98% power
• Output Linearity: 2%
• Power Limit Range: 0-100% of max load power
• Ambient Temperature Range: 0 to 50 °C
• Power Supply: 100-265VAC 50mA max.
• Line Frequency Range: 47 to 63Hz
• SCR Gate Drive Characteristics: Initial pulse peak current of 1.6A rise time of ~200nS, maintain current of 160mA; See the SCR gate drive profile section for more detail.
• SCR Drive / Mains Isolation: 2500Vrms
• SCR to SCR Isolation: 2500Vrms

5.3.1 Mechanical Dimensions

A diagram showing the top view of the PCM-1B board with dimensions. Key measurements include 3.300 inches height, 3.400 inches width, and 3.700 inches overall width. It indicates mounting hole locations (0.160" diameter, 4 places) and the maximum height of 0.8 inches. Components like SCR1, SCR2, DIP switches, and terminal blocks are labeled.

6. WIRING DIAGRAM - SINGLE PHASE

A single-phase wiring diagram for the PCM-1B. It shows connections for COMMAND INPUTS (analog, potentiometer, 4-20mA/0-10V), POWER LIMIT ADJUST, DIP SWITCHES, and the main power input (L1, L2). The diagram illustrates the connection of the PCM-1B to two SCRs (SCR1, SCR2) which control a LOAD. It also notes that an 'EXTERNAL SNUBBER REQUIRED FOR PROPER SCR TURN ON/OFF'.