Data Acquisition System | Keysight DAQ970A | DAQ973A

FAQ

Q1. How to Maintain and Improve the Lifespan of the Data Acquisition System (DAQ)?

Switches are a key part of a data acquisition (DAQ) system. A typical DAQ measures multiple channels and uses switches to connect multiple transducers to a single measuring device. It also uses switches to route power to electrical devices, or for signal routing within a device or between different instruments. They experience the most wear and tear over time and will eventually determine the lifespan of your DAQ system. Figure 1 shows a basic block diagram of a DAQ with the switches close to the input interface.

Figure 1. Data Acquisition System Block Diagram (Basic)

Switches play an essential role in streamlining test systems. Its benefits are:

1. Reduced test footprint and cost. You do not need dedicated measurement hardware for each transducer. Instead, measurement hardware is wired to many transducers via the use of switches.
2. Closed loop automated test system. You can use switches to control or route power to your device under test and measure the output of your device. You can streamline your control and measurement hardware significantly with switches.

Prolonging the life of your switches means extending the life of your DAQ system. Switches are built into your module interface cards as well as your DAQ mainframe. In this blog, you learn how to maintain and improve the lifespan of your DAQ by selecting the proper type of switches, predicting the life of your switches, and prolonging the life of your switches.

Q2. How do I choose the right switch?

Choosing the right switch for your application is important. You want to maximize the lifespan of your switches, hence, your DAQ system.

Armature switches are electromechanical relays that are rugged and can handle high- voltage and current inputs. They have very low contact resistance, but they are the slowest in switching speed when compared to other types of switches.

Reed relay switches are also electromechanical relays but are smaller and lighter in structure compared to its armature switch cousin. They switch much faster, have low contact resistance but lower power handling than armature switches.

Solid-state switches have broad power handling and medium to high-power capabilities depending on the field effect transistor (FET) components utilized. Their strengths are the high-speed switching capability and almost unlimited switching lifespan because of no wear and tear; since there are no moving parts.

Figure 2 provides a summary table comparing the critical characteristics of the armature, reed, and solid-state switches. Keysight’s new next-generation data acquisition system, DAQ970A offers three types of switches.

	Armature switch	Reed relay switch	Solid-state switch
Contact resistance	<1.0 Ω	<1.0 Ω	<50 Ω
Switch speed (channels/s)	<100	<300	<500
Life (no load)	100 M	100 M	Unlimited
Life (rated load)	100 K	100 K	Unlimited
Max. input (power)	50 W	2 W	2.4 W
Keysight’s DAQ970A input modules with respective switches	DAQM901A	DAQM902A	DAQM900A

Figure 2. Comparisons between armature, reed and solid-state switches based on DAQM9XXA multiplexer modules.

Q3. How do I predict the life of my switches?

The life expectancy of the switches is dependent on the types of load they carry. Different types of loads cause various in-rush current spikes; voltage arcing as a result from back electromotive force (back EMF), or from energy stored on the loads. They eventually shorten the lifespan of your switches. However, you can maximize and improve the lifespan of your switches by designing in a switch derating factor during your test development.

Switch derating factor means lowering the manufacturer’s ratings for a relay based on the load type. Figure 3 has the suggested switch derating factors for the various types of load.

Type of Load	Switch derating factor in percent
Resistive	75
Inductive	40
Capacitive	75
Motor	20
Incandescent	10

Figure 3. Switch derating factors for various types of load.

Most DAQs can help you track the lifespan of your switches. For example, Keysight’s DAQ970A has a relay odometer as shown in Figure 4.

Figure 4. DAQ970A relay odometer.

Q4. How do I prolong the life of my switches?

Over time, voltage arcing between switch contacts affects the reliability and lifespan of a switch. Other factors that affect switch contact reliability are high-power or high-voltage switching, thermal stress on the contacts, and the types of loads used.

You can take proactive actions to prolong the life of your switches. Extending the life of your switches means prolonging the life of your DAQ system.

For example, you can build suppression circuits to limit in-rush currents, resistor-capacitor networks, or R-C circuits to reduce transient voltages, and voltage clamp circuits.

Use a varistor when adding an absolute voltage limit across the relay contacts. Varistors are available for a wide range of voltage and clamp energy ratings. Once the circuit reaches the varistor’s voltage rating, the varistor’s resistance declines rapidly.

Summary

This blog has shown you how to choose the correct relay type, maintain your voltage current, and power ratings within the relay’s ratings derated as appropriate for a given load type, and add suppression circuits as required.

Keysight’s new DAQ970A data acquisition system improves scan rate of up to 450 channels/sec with new solid-state multiplexer module (DAQM900A) and reading speed per channel of up to 5000 readings/sec to memory and Input/output interface.

To learn more about the next generation DAQ970A and the solid-state multiplexer module, please visit our website, www.keysight.com/find/DAQ970A.

 To learn more about optimizing your DAQ for measurement speed, please read our article on How to optimize measurement speed of your DAQ.