User Manual

RedLab 1208LS User's Guide Functional Details

With all outputs at their maximum output current, you can calculate the total current requirement of the RedLab

1208LS USB +5 V as follows:

(RedLab 1208LS @ 20 mA) + (16 DIO @ 2.5 mA ea) + (2 AO @ 30 mA ea ) = 120 mA

For an application running on a PC or powered hub, the maximum available excess current is 500 mA−120 mA

= 380 mA. This number is the total maximum available current at the PC+5V screw terminals. Measurement

Computing highly recommends that you figure in a safety factor of 20% below this maximum current loading

for your applications. A conservative, safe user maximum in this case would be in the 300-320 mA range.

Since laptop computers typically allow up to 100 mA, the RedLab 1208LS in a fully-loaded configuration may

be above that allowed by the computer. In this case, you must determine the per-pin loading in the application

to ensure that the maximum loading criteria is met. The per-pin loading is calculated by simply dividing the

+5 V by the load impedance of the pin in question.

Ground terminals

The 10 ground (GND) connections are identical, and provide a common ground for all RedLab 1208LS

functions. Refer to the pinout diagrams

on page 16 for the location of the GND terminal pins.

Calibration terminal

The CAL connection (pin 16) is an output you should use only to calibrate the RedLab 1208LS. Refer to the

pinout diagrams on page 16 for the location of this pin. Calibration of the RedLab 1208LS is software-

controlled via InstaCal.

Trigger terminal

The TRIG_IN connection (pin 18) is an external digital trigger input. You can configure this terminal with

software for either trigger high or trigger low.

Counter terminal

Pin 20 (CTR) is input to the 32-bit external event. Refer to the pinout diagrams on page 16 for the location of

this pin. The internal counter increments when the TTL levels transition from low to high. The counter can

count frequencies of up to 1 MHz.

Accuracy

The overall accuracy of any instrument is limited by the error components within the system. Quite often,

resolution is incorrectly used to quantify the performance of a measurement product. While "12-bits" or "1 part

in 4096" does indicate what can be resolved, it provides little insight into the quality of an absolute

measurement. Accuracy specifications describe the actual results that can be realized with a measurement

device.

There are three types of errors which affect the accuracy of a measurement system:

 offset

 gain

 nonlinearity.

The primary error sources in the RedLab 1208LS are offset and gain. Nonlinearity is small in the RedLab

1208LS, and is not significant as an error source with respect to offset and gain.