The new SSR Mounted Phase Angle Controller Module SSRMAN-1P-CL mounts directly on the SSR input terminals and provides true linear power phase angle control of the load. The output power is based on the command input and the current feedback from the current transformer. The command can be dip switch selected from over seven different industry standard inputs. Using the SSRMAN-1P-CL with the appropriate SSR for your load will provide a modular high isolation SCR power control at a very low price. An extensive filtering scheme and proprietary zero cross detection algorithm improves noise rejection without sacrificing accuracy.
The new ZERO CROSS SCR GATE DRIVER NWZC-SCR, is a low cost SCR driver for driving back to back SCRs in resistive load applications. The driver board is zero cross fired and has on board MOV protection. It provides optically isolated 5V, 24V inputs that can easily be interfaced to temperature controllers and PLC Time Proportiong (PWM) outputs. The packaging is available in panel mountable or din rail mountable snap tracks.
SCRs requiring 200mA of gate current or less are a good fit for use with the ZERO CROSS SCR GATE DRIVER NWZC-SCR. Wiring of the Module is simple and requires no external power supply; the gate drive power is derived from the line supply of the SCRs.
Controlling TECs or Thermo Electric Coolers with standard off-the-shelf temperature controllers presents a challenge to the system designer. Pelteir devices require H-bridge drivers to provide heat and cool functions. The H-Bridge has to be designed to allow the heat and cool outputs of the temperature controller to steer the correct polarity of the DC power source into the TEC. The new TEC H-Bridge TCH1560 Isolated H-Bridge Amplifier makes the design task much simpler.
The temperature controller outputs interface directly to the optically isolated input as shown above. The power input is connected to the Thermo Electric H Bridge Controller TCH1560 and the TEC is connected to the output. Special shoot through prevention logic prevents the outputs from turning on at the same time even if both temperature controller outputs are on. With a frequency response time as fast as 1mS and a 60V 15Amp rating the TCH1560 presents a high performance and economical way to drive TECs in a heat cool configuration.
Phase Fired SCRs can generate significant 3rd, 5th & 7th order harmonics above the line frequency due to the thyristor firing occurring between the AC zero crossings:
When Phase Fired SCRs must be used due to the load characteristics described in our previous blogs, EMI filtering can be added to the line to attenuate the harmonics. Several companies makes suitable high current filters for Phase Fires SCRs:
By using the line filters with SCR Power Controls it is still possible to obtain suitable EMC performance and allow sales with a CE mark.
Commutation Problems: When an SCR or TRIAC is used to Phase angle 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.
Snubber Suppliers: Check out our new RCSB Snubber: RCSB SNUBBER which is also available for SCRs and well as SSRs.
Phase angle controllers should be used when the following conditions exist:
- The load requires voltage control
- The load may not be able to tolerate full line voltage so a phase angle w/voltage limit may be employed
- The load has high inrush characteristics and required soft start
- The load is inductive
- The load is sensitive to the thermal shock of time proportiong (burst firing)
- The load is very fast
- The load is a phase controllable motor or vibratory feeder
Burst Firing (time proportioning or PWM) at the zero crossings is a good method to control the load power when the following conditions exist:
- The load is a heating load and has sufficient thermal mass that the on and off pulses will not ripple through the process
- Low EMI is required
Soft Start is a method of limiting the rate of rise of the output of a phase angle controllers power output generally during start up only. Soft Change is a method of limiting both the rise and fall of of a phase angle control’s power output. Both of these methods are used mainly to limit the load’s inrush due to either the resistance temperature coefficient of a heater lamp or because the load is inductive. Soft start is useful on high inrush heaters such as Quartz, Molybdenum, Tungsten, or Graphite heaters. Soft Change can be a good choice for phase angle controlling inductive loads, where rapid changes in the phase angle can induce a DC imbalance in the in load and thus cause misfiring, heating in the inductor, or blown fuses.
Line Voltage Compensation in a Manually Controlled Heater Process: In a simple manually operated phase angle control arrangement the user sets the power level of the phase angle controller and this delivers a percentage of the full power to the heater. Ruling out any other process disturbances, the line voltage can change at any time affecting the power delivered to the heater dramatically (don’t forget P=E^2/R). Line voltage compensation effectively cancels out the change in line voltage keeping the power delivered to the load exactly where the user sets it.
Line Voltage Compensation in a Closed Loop Heater Process: In a closed loop heater process, a temperature controller such as a CAL 3200 sets the output level of the phase angle controller. The temperature controller (if it is a PID controller) will correct for changes in line voltage, but these changes have to ripple through the process lags before they arrive at the controller. This can affect the product quality, because often times the sensing point of the controller isnt perfect. Line voltage compensation cancels the affect of line voltage changes before they arrive at the temperature controller.
We provide custom solutions for laboratory temperature controls, Barbeque Bbq temperature control, and many different industrial controllers.
Please visit us from time to time as we will be adding many technical articles and application notes.