Note for all A-D converters: Modern Macs lack built-in serial ports, so you'll need a USB to serial converter and driver software. The units made by Keyspan (now, TrippLite), specifically the USA-19HS, function reliably with LabHelper. Other brands have not worked well, or at all.
Data Electronics DataTakers are expensive, rugged, and highly capable (although not particularly fast). Several models are available; all use the same (or very similar) basic instruction set and all are impressively versatile. They have only 5-12 numbered hardware inputs, but several different instrument outputs can be connected simultaneously to each input, greatly increasing the number of sensors that can be monitored.
An analog input on a DataTaker 800 has 4 connectors labeled #, +, - , and *. On a DataTaker 500 and related models, R is used instead of #.
- For differential voltage readings, connect your leads to the + and - terminals.
- For other voltage inputs (including thermocouples) connect the ground or neutral lead to # (or R) and the other lead to +, -, or *. When using thermocouples, be sure to indicate the thermocouple type (in the 'DataTaker inputs' window).
- Resistance measurements require two-wire connections to either the + and - or the * and # (or R) terminals.
You must use the 'DataTaker inputs...' option in the External A-D device submenu in the A-D menu to specify which connectors are in use, and for what purpose (volts, resistance, or thermocouples); this option is called automatically whenever you're using a DataTaker and add a new channel. You can also use the channel as a high-speed counter, but this involves a different set of inputs. Thus, one DataTaker hardware input can be used for several logical channels.
DataTakers come with screw terminals (DT50/500/600) or 'cage clamp' (DT800) terminals to which you can directly attach
instrument recorder cables. However, you may want to build your own
junction box with connectors that are easier to use -- especially if you change instrument inputs frequently.
DataTakers have the digital output channels necessary to control external devices, such as gas multiplexers. However, they use open collector outputs that may not produce enough positive voltage to act as a digital 'high' value. Adding this simple circuit will solve the problem. It can be powered by the onboard voltage source on DataTakers: +5V on a DT500 series or +12V on a DT800.
•
DT50, 500, 600 series The DT50 has 5 channels of high-resolution analog-to-digital conversion; the others in this series have 10 A-D channels;
the 600 series have an LCD display and simple keypad but are otherwise the same as the DT500 (note that early DT500s had a black case as shown in the picture below; this was changed in later models to a rather garish purple, as seen in the picture of a DT600 at left).
As described above, each A-D channel can be set up to read voltages, resistances, or thermocouples, or can be used as a digital counter. Four digital I/O lines are available (for controlling external devices).
These DataTakers can communicate at speeds of up to 9600 baud (4800 is recommended), and are limited to sampling rates of no more than about 5/sec for most applications.
Note: I have not tested all of the many versions of the DT50/500/600 series with LabHelper, but they should function similarly. I have used the DT500 fairly extensively and users report no problems with the DT50.
The cable joining these DataTakers to the computer (more specifically, to the USB --> serial converter) needs to have the correct connections. The wiring diagram in the DataTaker manual for IBM-compatible 9-pin (DB9) connectors works well.
Note: Because of their low sampling and communication rates, these DataTakers cannot be used in oscilloscope mode.
•
DT800 series The DataTaker 800 series are more modern, higher-speed versions of this sophisticated A-D converter.
The basic DT800 has 12 channels of high-resolution analog-to-digital conversion; each channel can be set up to read voltages, resistances, or thermocouples, or can be used as a digital counter. Eight digital output lines are available (for controlling external devices).
DataTaker 800s communicate at a default rate of 57.6 Kbaud and can handle 115.2 Kbaud, and hence can gather data faster than other DataTaker models. However, they're still fairly slow compared to the Sable UI-2. The DT800's conversion speed varies with the type of data (e.g., thermocouple or resistance readings take longer than simple voltage readings), but you can expect about 10 samples/sec on single channels in 'high accuracy' mode and 50 samples/sec in 'high speed' mode; additionally, there is a 'burst' mode that can take intermittent readings at sample rates of several kilohertz (go here and here for details).
The cable joining the DT800 to the USB --> serial converter needs to have the correct connections. The wiring diagram in the DataTaker 800 manual for IBM-compatible 9-pin (DB9) connectors works well. In brief, it requires two female DB9 connectors and 5 conductors:
• join pins 5 on both DB9s
• join pin 3 on one DB9 to pin 2 on the other, and vice versa
• join pin 7 on one DB9 to pin 8 on the other, and vice versa
Since the communication speed is fairly high, do not make the cable longer than a couple of meters.
Note: The DataTaker 800 can be used in oscilloscope mode, but maximum sampling rates are fairly low. The main constraint is the speed of the serial connection. Using the DT800 in oscilloscope mode is described in more detail here.