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The LJTick-RelayDriver (LJTRD) is a signal-conditioning module that allows two digital outputs to each control up to 50 volts and 200 mA. The 4-pin design plugs into the standardDIO/DIO/GND/VS screw terminal block found on newer LabJacks such as the U3 and UE9.
Extending from the back of the LJTRD are four pins. The first two pins provide +5 volt power and ground from the LabJack, although +5 volt power is not used by the LJTRD and thus is not connected to anything. The other two pins connect to digital I/O on the LabJack. The four pins plug directly into the 5.0 mm spaced screw terminals on the LabJack U3/UE9 as shown in Figure 2. The LJTRD should be plugged into a digital I/O block, as opposed to an analog I/O block.
The LJTRD has a 4-position screw-terminal providing the following connections:
RA/RB: The high side of each output switch. When IOA/IOB from the LabJack is set to output-high, the respective switch is closed. When IOA/IOB is set to output-low or input, the respective switch is open. Each switch can hold off up to 50 volts and can sink up to 200 mA.
GNDR: The low side of both output switches. Connected to LabJack GND via a 22 ohm resistor (resistor is on the LJRTD).
VR: Connect the load voltage to this terminal to bias the internal clamping diodes on each switch. If each switch has a different load voltage, the highest voltage should be connected to VR. The clamping diodes help suppress switching transients, and can be particularly important when dealing with inductive loads such as mechanical relays or solenoids. Although this connection is optional, there is usually no reason not to use it.
When connecting a relay or other type of load, there will be a voltage drop depending on current. Below is a chart which represents the voltage drops that can be expected at various currents.
If operating at high frequencies, please note the following table. As current through the RelayDriver increases, the cutoff frequency also increases, which means that if you encounter problems at high frequencies, the load resistance should be decreased to allow more current to flow through the RelayDriver. This behavior is almost never a problem when controlling relays, since relays typically draw 3 to 20mA, and the LabJack U3 will not output a PWM frequency exceeding 732Hz.