DMS-30DR

DMS-30DR meters are highly versatile devices that can be used in hundreds of applications. The application circuits chosen for this section have historically received many inquiries. Every attempt has been made to ensure technical accuracy, and all of the following circuits have been prototyped and tested to ensure functionality. Please keep in mind, however, that real-world applications are seldom as straightforward as the approaches presented here. Most applications have many more components - and many more connections - than the illustrations show.

The simplified schematic shown in Figure 1 can be very useful when debugging a malfunctioning panel meter circuit, particularly if the user has some knowledge of operational amplifiers (op amps). The meter's high-impedance input consists of an op amp powered from a ±5Vdc power supply (the 5V is internally generated). Knowing this, one can easily see why input signals applied to () INPUT LO and (+) INPUT HI have to be kept within the power supply rails of ±5V. Also note that only pin 11 has a current-limiting 909k series resistor. High input voltages that have a common ground with pin 3 (5V RETURN) should only be applied to pin 11 ((+) INPUT HI) and never to pin 12. In these high-voltage cases, pin 12 should always be tied to pin 3 (5V RETURN).

One of the simplified schematic's noteworthy features is that it shows internal voltage values. It also shows that pin 3 is the meter's zero-volt reference point - regardless of the type of power or signal source used. This is an important point to keep in mind when a digital or analog multimeter is used to make system measurements. The multimeter's negative lead (usually the black one) must be connected to pin 3 (5V RETURN).

C&D Technologies' new DMS-30DR Series are the first digital panel meters to offer LED displays that are readable in direct sunlight-no special filters or shading devices are required.

Their Autodim circuit automatically adjusts the display's brightness to suit viewing environments ranging from total darkness to full, brilliant sunlight. A user-accessible brightness adjustment pin enables custom intensity settings or display matching in multiple display applications. Washed out, hard-to-read digital readouts are a thing of the past!

Until now, users whose instrumentation required daylight visibility had to settle for less reliable LCD display technology. However, in order to remain legible in low ambient light, LCDs require complex, power-hungry backlighting circuitry. And, these displays typically suffer from very narrow viewing angles. In contrast, DMS-30DR Series LED-based displays' power consumption drops as ambient light decreases, and their viewing angle extends to nearly 180 degrees vertically and horizontally.

All models operate from a single +5V supply, and draw as little as 7mA when operated in total darkness-that's less than 1/10 Watt. At maximum brightness power consumption is typically less than 200mA (1 Watt). DMS-30DR voltmeters are available in four differential input voltage ranges: ±200mV, ±2V, ±20V and ±200V. Input impedance is 1,000 megohms for the ±200mV and ±2V inputs and 1 megohm for the ±20V and ±200V inputs. CMRR for all devices is 86dB, and inputs are overvoltage protected to ±250V. Each meter incorporates a precision, ultra-stable voltage reference and is factory calibrated prior to encapsulation.

The small size (2.17" x 0.92" x 0.56") of DMS-30DR meters is achieved by integrating their display, Autodim display drivers, light sensor, reference circuit, and A/D converter into in a rugged epoxy-encapsulated assembly. The device's 12-pin, component-like, DIP package is both vibration and moisture proof, making them ideal for harsh environments. Each package incorporates a built-in color filter and bezel, and is easily mounted in either panels or pc boards.