The LJTick-Divider (LJTD) is a signal-conditioning module designed to divide 2 single-ended channels of higher voltage analog signals down to 0-2.5 volt signals. The stock builds are for 0-10 volt inputs (UNI10V) or ±10 volt inputs (BIP10V). The 4-pin design plugs into the standard AIN/AIN/GND/VS screw terminal block found on newer LabJacks such as the U3, U6, and UE9. The use of large resistors and a precision op-amp buffer provide an input impedance of 1 MΩ. By adding or replacing resistors, many other configurations are possible.
Prior to December 2007, all shipped LJTick-Dividers were the UNI10V configuration and were not specifically labeled. Starting December 2007, all shipped LJTick-Dividers have a label specifiying UNI10V, BIP10V, or other.
VINA/VINB: These screw terminals are for the 2 single-ended channels of input analog voltages. With the factory default configurations (UNI10V or BIP10V), the input to either of these terminals is typically 0-10 or ±10 volts, and produces 0-2.5 volts on the respective OUT pin.
GND: Same as LabJack ground. VINA/VINB must be referred to this ground.
VREF: A 2.5 volt reference voltage output. Internally this reference is used for level shifting, but very little current is used, leaving substantial current available to the user if a very accurate 2.5 volt reference is needed.
The above figure is a schematic for one channel of the LJTD, showing the standard factory installed values for UNI10V. The input/output relationship is described by the below equation, assuming the op-amp is in the default unity gain configuration.
The resistors R1+R2, R3, and R4, can be changed to provide other ranges as shown in the table below. The table shows the input voltage at the typical output voltage limits of 0.0 and 2.5 volts. It also shows the input voltage for an output voltage of 3.5 volts, as the internal buffer amplifier accepts a maximum input voltage of 3.5 volts when powered by VS=5.0 volts, and thus when the amp is configured for unity gain the maximum output voltage is 3.5 volts. The Slope and Offset columns go with the formula Vout = Slope*Vin + Offset. The labels in the Name column are used when ordering custom configurations.
The packages for resistors R1-R4 are 0805, while all other resistors and capacitors are 0603. The tolerance of the factory installed resistors is 0.1%, so a good option for the 180k resistor below would be digikey.com part number RG20P180KBCT.
U3: The LJTD is generally used with low-voltage channels on the U3-LV or U3-HV. The nominal input range of a low-voltage channel is 0-2.44 volts, so the input range provided by the LJTD is from the "VIN (OUT=0)" column to a little less than the "VIN (OUT=2.5)" column. For example, the UNI10V in this case will provide an input range of about 0 to 9.76 volts. If you set the U3 analog input to the "special" range it takes an input of about 0-3.6 volts, so the input range provided by the LJTD is from the "VIN (OUT=0)" column to the "VIN (OUT=3.5)" column. For example, the UNI10V in this case will provide an input range of about 0 to 14 volts.
U6: The LJTD is used with the +/-10 or +/-1 volt range on the U6. With the +/-10 volt range the full 0-3.5 volt output of the LJTD can be measured, but only 3.5/20 = 17.5% of the U6 input range is used. With the +/-1 volt range, the 0 and 1 volt output columns above apply, and 50% of the U6 input range is used.
UE9: The LJTD is used withe the 0-2.5 or 0-5 volt range on the UE9. The 0 and 2.5 volt output columns above use 100% of the 0-2.5 volt UE9 input range, or the 0 and 3.5 volt columns use 70% of the 0-5 volt UE9 input range.
(1) The maximum input voltage to the buffer amplifier is VS-1.5, so for proper operation with signals up to 2.5 volts, VS must be greater than 4.0 volts.
(2) The input impedance and bias current is dominated by the input resistors not the buffer amplifier. The input bias current of the internal buffer amplifier is less than ±200 pA across the voltage range, which is an important number as far as sizing the input resistors to not create excessive offset.
Declaration of Conformity
Manufacturers Name: LabJack Corporation
Manufacturers Address: 3232 S Vance St STE 100, Lakewood, CO 80227, USA
Declares that the product
Product Name: LJTick-Divider
Model Number: LJTD
conforms to the following Product Specifications:
EMC Directive: 89/336/EEC
EN 55011 Class A
EN 61326-1: General Requirements
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Thank you for the quick response. :) Much appreciated.—Robert, University of Missouri