Analog Input Products

Analog input boards are useful for measuring variably changing conditions in the real world. When we want to measure these variably changing conditions, we need analog inputs to convert these changing real world conditions to changing electrical quantities. For example, monitoring the temperature inside a wood kiln, or the water pressure on the output of a pump, or the heart rate of a medical patient. In each of these cases, you can use one of our analog input devices to convert the electrical data from a sensor or transducer into binary data that can then be used by your computer. The device that converts this data is known as an analog to digital converter (abbreviated ADC, A/D, or A to D). An analog input is a measurable electrical signal with a defined range. The analog input changes continuously in a definable manner in relation to the measured property. This data is very useful for process monitoring, process control, or simple monitoring / data collection and acquisition. ACCES' analog input boards amplify and multiplex input signals from thermocouples, strain gauges, accelerometers, photo sensors, flowmeters, RTDs, thermistors, voltage sources, millivolt sources, and current sources, just to name a few.

There are basically three types of analog input signals used to measure these conditions. They are voltage, current, and resistance.

Voltage Mode Connections...

If voltage mode is used, analog input connections can be either single-ended or differential. Low per-channel cost is a major advantage of using single-ended inputs because only one multiplexer switch is needed per channel and there is less system wiring. Single-ended inputs all share a common return or ground line. The measurement is the difference between the signal and the ground. Only the "high" signal wires are connected through the amplifier and multiplexer. The "low" wires return through the system ground connections. That is, both the signal source and the amplifier are referenced to ground. This arrangement works fine as long as the ground potential difference is very small. However, if there is a large difference in ground potential, extraneous currents can flow and generate errors. This is called a "ground loop". Ground potential differences (ground loops) can cause larger interference problems than electromagnetic fields. Ground loops occur if the sensors are tied to a local ground. That local ground can be many volts different from the ground potential at the receiving circuit. Single-ended measurements are also more susceptible to noise than differential measurements due to differences in the signal paths and the tendency to pick up surrounding electrical activity. With single-ended inputs you have no way of distinguishing between the signal and the noise.

To avoid this problem, a differential-input connection can be used with an amplifier that has a high common mode rejection ratio. A differential arrangement connects both ends of the signal source to the inverting and non-inverting inputs of the amplifier. Measurement is the difference in voltage between the input and the reference, which helps to reduce noise and any voltage that is common to both wires. Twisting wires together will ensure that any noise picked up will be the same for each wire. In this way, voltage due to ground loops appears as a common mode voltage and can be rejected by the common-mode-rejection properties of the amplifier. An instrumentation type amplifier (rather than a simple operational amplifier) is required and two multiplexer switches are required per channel. An obvious disadvantage of differential inputs is that you need twice as many wires, so you can connect only half the number of signals, compared to single-ended inputs.

If you have signals larger than 1V, short signal wires, and close together signal sources, single-ended inputs should be fine. If your application falls outside these boundaries, differential inputs would be the wise choice.

Current Mode Signal Connections (e.g. 4-20 mA or 10-50mA inputs)...

Resistance Mode Connections...

Signal Conditioning...

Signal conditioning is an essential requirement in many applications and systems which demand accurate and precise measurements. Signal conditioning circuits convert one type of electronic signal into another type of signal that can be used to improve and enhance the data acquisition system and application. Sometimes the data acquisition card that you plug into the computer provides necessary conditioning; sometimes that signal conditioning must be done external to the computer. In general, signal conditioning consists of amplification, isolation, filtering, sensor excitation, cold-junction compensation and more.

Signal inputs accepted by our signal conditioners include DC voltage/current and AC voltage/current. Sensor inputs can be accelerometer, thermocouple, thermistor, resistance thermometer (RTDs), strain gauge or bridge, and LVDT/RVDTs. Signal conditioned outputs include voltage, current, frequency, relay, isolation, and more.

ACCES offers a wide variety of external signal conditioning products which include analog, digital, and serial signal conditioning. Sometimes the data acquisition product you plug into the computer provides the necessary conditioning; and sometimes that signal conditioning must be done external to the computer.

Click the following wikipedia links to learn more about analog inputs, signal conditioning and data acquisition in general.

PC/104 Multifunction Analog Input/Output DAQ Products

A small form factor (3.6 x 3.8 in) computer board intended for use in embedded PC systems, these rugged self stacking modules allow for an expandable system without the burden of a backplane with a fixed number of slots. Some sample applications for this type of technology include the following: vending machines, test equipment, medical instruments, communications devices, vehicular systems, data loggers, aviation, military applications and industrial control systems.

PCI Multifunction Analog Input/Output DAQ Products

ACCES' PCI/PCI-X bus data acquisition and control (DAQ) cards are designed to cover the most common industry applications. Our full selection of PC-based plug-in analog and digital I/O, multifunction, isolated, relay, serial, and watchdog cards guarantees we'll have a product to match your application. The broad availability of the PCI bus makes it one of the most popular options for industrial/rack-mount DAQ systems.

USB Multifunction Analog Input/Output DAQ Products

Select from a large assortment of 16, 32, 64, 96, and 128-channel multifunction analog input modules. Analog inputs are available as either single-ended or differential. Choose from either 12 or 16-bit versions with speeds up 500kHz. All models incorporate two 16-bit analog outputs, 16 lines of digital I/O, and are integrated inside a rugged, small sized steel enclosure with an anti-skid bottom. A DIN rail mounting provision is available for installation in industrial environments. Additional features include software autocalibration (real-time) and on-board references for increased accuracy. Extended temperature (-40° to +85°C) is available.

A wide range of flexible signal conditioning types per channel are also offered. These include options such as RC filters on each input, voltage dividers on each input, 4-20mA current inputs, thermocouples (temp sensor for cold junction), RTD measurement, as well as bridge completion.

For applications requiring analog inputs only, a line of cost efficient USB products offers all of the features described above except no analog outputs are included.

USB OEM (board only) Multifunction Analog Input/Output DAQ Products

ACCES now offers USB-based data acquisition and control in both standard packaging and embedded OEM USB/104 board only options. These USB devices are perfect for a variety of applications requiring monitoring, control and industrial serial communications. USB is by far the most popular and compatible standard data interface for direct PC connection. Add the features you need in your application in hours, not days. Choose from over 100 different models and options (including extended temperature) encompassing analog I/O, digital I/O, counter/timer, and serial I/O configurations. Experience simple and immediate connection to any PC or embedded system with a USB port.

Our USB OEM product line features two different size form factors - USB/104 and USB/PICO. The USB/104 product line PCB size measures just 90mm x 96mm and the mounting holes match the PC/104 form factor for quick and easy installation in both new and existing PC/104-based systems. Our USB/PICO line was created for our customers which demand an even smaller footprint and certain specific I/O configurations. The size of these modules is exactly half that of PC/104 (72mm x 60mm) and can be mounted virtually anywhere, including Pico-ITXe next generation embedded CPUs. Both USB/104 and USB/PICO are stackable or unstackable, making them one of the most versatile I/O form factors currently available.

Remote ACCES Analog Input/Output DAQ Products

Sometimes your sensors or the piece of equipment you are trying to control is not in a convenient place to have a PC close by. The sensors may be widely distributed through out your plant and it just wouldn't be cost effective to run all your wiring to where the PC is. In addition, low level signals are more accurately acquired when digitized close to the signal source. In all these cases our REMOTE ACCES line of products will help. The REMOTE ACCES pods are intelligent, sensor to computer interfaces. Each pod can be used as an autonomous data logger to acquire data for later download. Or as many as 31 pods may be connected on a single two wire multidrop RS-485 network allowing a cable distance of up to 4000 ft. You can also go wireless and extend your range by adding RS-485 wireless transceivers to your serial port. Each unit comes in a rugged NEMA 4 enclosure and can withstand harsh industrial and marine environments.