Usually you connect to the serial port of the computer using a female DB9 or female DB25 connector. Also referred to as a female 9 pin, or female 25 pin, D-shell connector. The serial port is RS232C (or RS-232C). RS232 stands for Recommended Standard number 232, and the C stands for revision C. Each RS232 device at our site connects to an RS232C serial port through a cable you provide (unless otherwise noted). 3 wires are generally used: Signal Ground, Trasmitted Data (TD), and Received Data (RD), otherwise referred to as Ground, Transmit and Receive. At both ends of the cable, pin 1 is Ground. At the computer, Receive is pin 2, while at the peripheral (e.g., temperature controller) it is pin 3. At the computer, Transmit is pin 3, while at the peripheral it is pin 2. The connection is made via "twisted pair" - which means the Transmit and Receive lines are twisted around each other along their length, from one end to the other. For the cable, solid copper wire is preferred over stranded wire simply because there are no strands at the end that can break off, or bend out, and short the connection. With appropriate converters you could connect by other means, such as infra-red light (e.g., IrDA).

RS485 (Recommended Standard 485) is specified to handle up to 32 devices in one loop. The "loop" is a length of 2 or 3 wires: +, - and ground. The devices tap into the wires along their length. The end of the + and - pair of wires is terminated with a resistor. Modern ICs used as an interface to the loop can sometimes handle more that 32 devices on one loop. It is sometimes possible to have 64 or 96 or more devices on the same loop. With RS232/RS485 converters, each loop uses one of the computer's COM ports. Baud rates greater than 100,000 baud are possible depending on the computer and the operating system. An edge connector allows you to attach a cable for the RS-485. 2 wires minimum [A and B, or (+) and (-)] are usually needed but COMMON is provided as well. Any untwisted wire is fine for a short run, but best, especially for long runs, is shielded, twisted pair, 120 Ohm characteristic impedance cable. for more detailed information see our library document RS-485 Serial Interface.

Definition of Ambient Temperature

"The temperature of the atmosphere, liquid, or other medium surrounding an object."
Source: The World Book Dictionary, © 1966 by Doubleday & Company, Inc.

Low Ambient Operating Temperatures

Almost all of our temperature controllers will function at ambient temperatures down to -20ºC (-4ºF).

Many designs will accept a -40ºC (-40ºF) operating ambient. Custom controllers can be built to operate down to -55ºC (-67ºF).

Operation at the low ambient is determined by the ICs used and their ability to have the correct gain and stable states. The output or load circuit may require increased drive to turn on. Any design that is specified to a low ambient operating temperature has been tested and shown to provide sufficient output drive at that temperature.

High Ambient Operating Temperatures

The high temperature is harder to define than the low, because the high ambient operating temperature depends upon the controller power dissipation and the heat sink dissipation.

For all our Pulse Width Modulated (PWM) controllers the following applies: The power dissipation of the controller is largely a function of the load current, and only slightly a function of the input voltage. Example: A unit running at 28v and 25 amps will dissipate the same power into the base as one which is 12v and 25 amps, however reducing the load current to 12.5 amps will reduce the power dissipation into the base by 1/2.

For an analog controller, the standard 1/4 power point analysis applies when determining power dissipation.

Specific Examples

TECC: The TE controllers are limited by the base plate (mounting bracket) temperature, because this is the heat sink for the bi-phase H-Bridge. Under full load the controller will be dissipating approximately 15 watts into the base plate, Therefore, if the controller is operated at elevated temperatures you need to provide additional heat sinking for the base plate. At laboratory temperatures (room temperature, about 20ºC or 70ºF) the controller will reach about 75ºC under full load. So if you provide an additional heat sink which results in, say. 70ºC in a 50ºC ambient, the controller will still function appropriately.

Model 5C6-353: This Laboratory Benchtop Temperature Controller with a 10 Ampere maximum output is designed to run in a laboratory environment. Maximum ambient operating temperature is 35ºC to 40ºC (95ºF to 104ºF).

Model 5C6-355: This Laboratory Benchtop Temperature Controller with a 15 Ampere maximum output is designed to run in a laboratory environment. Maximum ambient operating temperature is 30ºC (86ºF).

Model 5CX-140: The 5CX-140 series of controllers have a "derating curve" (see below) on the customer drawing that is defined by the temperature of the case.

5CX-140 Series Derating Curve

Sensors, TE modules, power supplies, device drivers, cables, etc. may be available for this product but are not included in the pricing.

ZERO VOLTAGE SWITCHING
(or ZERO VOLTAGE FIRING)

Zero Voltage Switching means that the power to the load (heater or cooloer or other device) is switched on or off only when the output voltage is zero volts.

Zero Voltage Switching can extend the life of a controller and of the load being congtrolled.

Controllers with Zero Voltage Switching use triacs or other solid-state relays instead of mechanical relays, and, in fact, all of our temperature controllers which use a triac are inherently Zero Voltage Switching.

With AC current, the voltage is zero 50 to 60 times per second. For example, with 120VAC at 60Hz the voltage swings from 0 volts to -120 volts to 0 volts to +120 volts and back to 0 volts 60 times per second. The controller only turns the power to the load on or off when the voltage is zero. (Since the cycle described above repeats itself, there are, at 60 Hz, 120 times every second that the AC voltage is at zero volts and power switching can occur.

With DC power, as used with thermoelectric controllers, the DC voltage is first converted by the controller to DC PWM (DC voltage that is Pulse Width Modulated). The voltage repeatedly goes from a positive or negative voltage to zero volts, and so this type of output power can also be switched on or off when the voltage is zero. The frequency of these pulses is high enough that the effecton the peltier device approximates that of DC power (without pulsing), and so pulsing the voltage in this way does not harm the peltier device.

Zero Voltage Switching has an advantage over the kind of switching that would normally be accomplished with a coil relay beacuse there is a reduced chance for electrical arcing. A relay could turn te power on when the voltage is high and then an electrical arc (spark) could result.