Out in Front: September 2, 1996

Few signal-conditioning and remote-data-acquisition pro-duct lines go to the lengths that Keithley Instruments' Intelligent Links do in providing compatibility with customers' data-com- munication networks. The 1×1×6.5-in. Intelligent Links modules provide solderless terminals for connecting a variety of transducers and sensors. The modules condition the sensor outputs, provide transducer excitation where needed, and convert the sensor outputs to digital form. They also perform functions such as linearization, unit conversion, and limit checking and provide an interface with in-house networks. Although the modules' intelligence and decision-making capabilities minimize network traffic, memory in the modules retains thousands of raw measurements, often allowing de-tailed after-the-fact analysis of conditions preceding an emergency.

The product line currently supports 16 network types, including RS-232C, RS-422, RS-485, and five varieties of Ethernet. You specify the network type when you place an order. Each module handles multiple channels; the number of channels varies with the module type. Cost ranges from $550 to $2200 per module—equivalent to $65 to $120 per channel.

Besides low- and high-level dc and ac voltages and currents, the modules handle measurements such as strain, force, weight, pressure, temperature, humidity, torque, rotations per minute, and power. Some modules provide hundreds of volts of ohmic isolation from channel to channel and from inputs to output and ground. ADC resolution varies from 8 to 20 bits, depending on the module function and conversion speed. Resolution and speed also determine the type of ADC a module uses—successive approximation or delta-sigma. Module power comes from a dc supply, which you can provide yourself or buy from Keithley. Keithley offers ac-line-operated supplies that power varying numbers of modules. The modules meet specification over a supply-voltage range of 7.5 to 30V.

Calibrating many remote data-acquisition systems is difficult. The only indication of the measured values is at the host PC, which can be thousands of feet from the transducer. Adjustments thus require two people—one at the PC, the other at the signal conditioner—communicating via a telephone or walkie-talkie. Keithley solves this problem by providing an RS-232C interface on every module and several user-interface devices that communicate via RS-232C. One of these devices is a palmtop computer containing the user-interface program on a plug-in PCMCIA card.

—by Dan Strassberg

Keithley Instruments, Cleveland, OH. (800) 552-1115, fax (216) 248-6168, product_info@keithley.com, http://www.keithley.com.