Data Acquisition / Oscilloscopes / Memory Recorders

While Memory Recorders don’t have sampling speeds that are as fast as those of digital oscilloscopes, these waveform recorders can be used to record various types of signals without worrying about potential differences between them and without using isolation amplifiers.

01. What is a Memory HiCorder?

Basic principle of Memory HiCorders

Typical waveform recording instruments have included the oscilloscope, electromagnetic oscillograph, and pen oscillograph (a category that includes pen recorders). With progress in digital technology, analog oscilloscopes gave way to digital oscilloscopes, while electromagnetic oscillographs and pen oscillographs gave way to memory-based recorders (transient recorders).
The Memory HiCorder is such a memory-based recorder. Figure 1-1 illustrates the basic architecture used by Memory HiCorders, which consist of A/D converters, data memory, a waveform display, and a printer along with a CPU that controls them. The A/D converters function to convert input analog signals into digital signals, which are then stored in the instrument’s memory and displayed or printed as waveforms.

Comparison with analog recorders

This section explains why analog pen oscillographs (pen recorders) and electromagnetic oscillographs were replaced by Memory HiCorders.

Pen oscillographs are self-balancing recorders with servomotors that operate in proportion to the amplitude of input signals to move pens and thereby record signal data. They have a response speed on the order of dozens of hertz, but their use of mechanical means to represent amplitude imposes limits on that speed, and ink-type variants require regular maintenance.

Electromagnetic oscillographs use high-sensitivity reflecting elements that are deflected according to the amplitude of the input signals in order to reflect light from a light source onto photosensitive recording paper. This method of measurement is capable of attaining high-speed recording with paper feed speeds of up to 200 centimeters per second (5 ms/cm) and response speeds on the order of several kilohertz, but it suffers from difficulties in the form of the high running costs associated with the photosensitive paper (resulting from the instrument’s high speed) and handling of the reflecting elements.

Memory HiCorders incorporate a thermal dot array printer (with a high resolution of 8 dots per millimeter) for printing recorded data, and this design offers high reliability due to the absence of moving parts such as pens. The instruments generally offer high response speeds, with sampling speeds of up to 20 MS/s (50 ns). They also combine extensive trigger functionality with low running costs, since users can retrieve only that waveform data which is necessary. Despite enhanced functionality and performance, the instruments have fallen in price, and for these reasons they have displaced electromagnetic oscillographs and pen recorders.

Memory HiCorder part names and functions

Memory HiCorders provide a color LCD for displaying waveforms and a printer for printing them. Both the display and printer can generate output in real time for certain signal loads. (Data acquired at a sampling speed of at least 10 kS/s is displayed on the screen in real time.)

With a maximum sampling speed of 20 MS/s, Memory HiCorders are slower than digital oscilloscopes, but they are characterized by the ability to accept input of numerous signals without use of isolation amplifiers or concern for potential differences between signals.

Recorded data can be stored on the instrument’s built-in SSD, a CF card, or a USB flash drive.

Each input unit generally provides two channels of input, and the instrument can accommodate input of up to 1000 V DC (700 V AC) as well as dynamic strain, thermocouple, logic, and other input simply by switching input units.

By connecting the instrument to a computer via its USB or LAN interface, users can transfer data and control the instrument remotely.

Memory HiCorder applications (Difference from digital oscilloscopes and data loggers)

Currently available recording and waveform observation instruments can be broadly divided into three categories: oscilloscopes in the high-speed segment of the market, Memory HiCorders in the medium- and low-speed segment of the market, and data loggers in the low-speed segment of the market. Customers choose instruments based on the frequency of the signal waveform being measured and recording interval, or based on characteristics such as input signal voltages, if the circuit being measured has a different ground potential.

While digital oscilloscopes excel in their ability to observe high-speed phenomena, their use of a common ground for all channels introduces the risk of shorts between circuits and ground faults when measuring circuits that are at different potentials relative to ground or when measuring targets such as mechatronic control circuits that mix strong and weak currents.

Since Memory HiCorders use isolated channels, they are able to perform tasks such as measuring DC control signals while observing a commercial power supply’s AC waveform or recording waveforms between inverter or converter inputs and outputs. As a result, they shine in applications involving measurement of circuits mixing strong and weak currents, as mentioned above.

Thanks to improvements in sampling speeds, Memory HiCorders have frequency characteristics that exceed the audible frequency range, and as discussed above, an extensive range of input units gives them capabilities ranging from electrical measurement to measurement of mechanical and vibration physical properties. Figure 1-6 illustrates the frequency bands for signal waveforms and compatible waveform measuring instruments in a variety of fields.

  

02. What is the Difference Between a Digital Oscilloscope and a Memory HiCorder?

No need for isolation amplifiers

The biggest difference between Memory HiCorders and digital oscilloscopes lies in isolation of input channels from one another and from the instrument.

A Memory HiCorder’s input channels are all electrically isolated. In a digital oscilloscope or A/D board, one side of each input channel is connected to the ground.

Digital oscilloscopes are well suited to use in applications where it is necessary to observe multiple signals that share the same ground, for example in measuring the electrical signals on a circuit board. However, if it were used to simultaneously measure the input and output sides of a power conversion device (such as a converter or inverter) like that shown in Figure 2-1, a digital oscilloscope would experience an internal short-circuit.

Memory HiCorders are extremely useful in applications such as this where a large number of signals at different potentials must be measured.

The only way to use a digital oscilloscope in such applications is to place an isolation amplifier between each signal and the instrument.

  

Difference of resolution and accuracy

Most digital oscilloscopes have a resolution of 8 bits (yielding 256 points). For example, if using a ±10 V range, that means the smallest interval that can be detected by the instrument is 0.078 V (obtained by dividing the full span of 20 V by 256 points).

Most Memory HiCorders have a resolution of 12 bits (yielding 4,096 points), enabling them to read values at an interval of 0.0048 V under the same conditions. A Memory HiCorder with a resolution of 24 bits would be able to read values at an interval of 0.000001192 V.

Memory HiCorders also offer superior accuracy. Whereas a typical digital oscilloscope provides accuracy of ±1% f.s. to ±3% f.s., Memory HiCorders deliver accuracy of ±0.01% rdg. and ±0.0025% f.s. to ±0.5% f.s.

This level of resolution and accuracy makes it possible to observe output from mechanical displacement, vibration, and other sensor types at a higher level of detail.

More channels and support for a larger variety of signals

Whereas typical digital oscilloscopes have 4 input channels, Memory HiCorders can accommodate from 2 to 54 channels of input, depending on the model.

In addition, different input units can be used, enabling Memory HiCorders to accept a larger variety of signals.

Available input units include analog units that can accept 1000 V DC (600 V AC) voltage input; units that can be connected to thermocouples, strain gauges, and acceleration pickups; and units that can be connected to high-precision current sensors.

Other units go beyond signal input to enable signal output with function generator and arbitrary waveform generation functionality.

Memory HiCorders shine in the field of mechatronics, where they deliver functionality that lies beyond the capabilities of digital oscilloscopes, for example in mixed recording of voltage and current waveforms and control signals for motors, inverters, and converters and in recording gasoline engine strain and ignition waveforms.

03. Basic Measurement Functions of a Memory Hicorder

Memory HiCorder basic measurement functions

Each Memory HiCorder provides enough functionality to be used as a number of different types of measuring instrument.

■ Memory recorder function
The instrument can record high-speed transients and sudden phenomena whose timing is unknown. It can also perform a variety of waveform calculations.

■ Recorder function
Although the instrument can be used as a real-time recorder or normal recorder, its extremely fast response speed, which is on the order of several microseconds, also enables it to record the amplitude of phenomena such as noise, even at low speed settings.

■ RMS recorder function
The instrument can record RMS voltage levels of current input without an RMS converter, and it can record fluctuations in supply voltage.

■ XY Memory・XY Recorder Function
The instrument can be used as an X-Y recorder for data from multiple X-T (time axis) recorded channels, with a user-specified channel as the axis.

■ Recorder&Memory Function
Recorder functionality can be used to record long-term fluctuations, and memory recorder functionality can be used to record sudden phenomena.

■ FFT Function
The instrument can analyze the frequency components of phenomena such as vibrations using its frequency analysis function.

■ Logic Recording Function
In addition to analog input, the instrument can record logic. Mixed digital/analog recording makes it possible to measure characteristics such as sequence timing.

04. The Power of Triggers

Trigger function and trigger types

The trigger function plays an important role in configuring a Memory HiCorder. When recording high-speed transients, this functionality makes it easy to start and stop measurement based on complex patterns that would be impossible for a human operator to duplicate manually.

The following introduces some Memory HiCorder trigger functions.

Figure 4-1 illustrates the types of trigger sources supported by Memory HiCorders. With the exception of manual triggers, triggers are activated based on AND/OR conditions between sources. Triggers can also be activated based on AND/OR conditions between analog channels and between logic channels.

■ Level Trigger
The level trigger is activated when the input voltage either rises above or falls below a set trigger level. A trigger filter can be set to keep the trigger from being activated by noise or other phenomena.

■ In-Window Trigger
Triggering occurs when the signal enters (IN) the defined upper and lower threshold range.

■ Out-of-Window Trigger
Triggering occurs when the signal exits (OUT) the defined upper and lower threshold range.

■ Voltage dip Trigger
Phenomena such as momentary voltage dips and power outages can be detected using a trigger designed specifically for use with commercial power supplies (50/60 Hz). The user sets a peak value (or an RMS value), and the trigger is activated if input falls beneath that level.

■ Period Trigger
Triggers can be activated when the period is outside of the specified time width, based on frequency variation and so on.

■ RMS Trigger
Triggers can be activated based on RMS levels.

■ Logic Trigger
Triggers can be activated according to signal input on logic channels.

■ Timer Trigger
Triggering occurs at the specified interval from the specified Start time until the Stop time.

Start　　‘00-1-1 0:00
Stop　　 ‘00-1-2 0:00
Ineterval   1:00

■ External Trigger
The external trigger is activated based on an external signal. The trigger is activated using a no-voltage contact signal or a 5 to 0 V signal. The external trigger has two inputs and outputs so that trigger output can be connected to another Memory HiCorder to enable simultaneous trigger operation.

■ Manual Trigger
Triggers can be activated by pressing the manual trigger key.

  

Trigger mode

Select from the below setting modes whether to record one recording length per trigger event, or to record continuously.

■ Single mode
Only one trigger activation is accepted by the instrument. When the trigger activates once, the waveform is recorded for the set recording length, and then measurement stops.

■ Repeat mode
Repeated trigger activations are accepted by the instrument. When no trigger has been activated, the instrument enters the trigger standby state.

■ Auto mode
Repeated trigger activations are accepted by the instrument. If no trigger is activated after approximately 1 s, the instrument automatically records the waveform for the recording length.

Trigger start point (Pre-trigger)

The user sets the trigger point as a percentage, using the recording start point for the set recording length as 0% and the recording stop point as 100%. By setting this pre-trigger, it is possible to review conditions before the trigger (malfunction or anomaly) occurred.

05. How to Use Memory HiCorders・Setting Examples

Example applications in different industrial fields

1. Electrical and power-related
•    Power supply analysis (momentary power outages, momentary voltage dips, power supply noise, harmonic analysis)
•    Analysis of problems with electrical control systems
•    Analysis of the characteristics of breakers and magnetic circuit interrupters
•    Detection of short-circuits and ground fault circuits
•    Generator and load dump testing
•    Battery charge/discharge testing
•    Servomotor and feedback system analysis
•    Analysis of magnetic card playback signals
•    Analysis of inverter input and output

2. Automotive, rail, and transport
•    Automobile and engine control testing
Engine combustion analysis, ECU signal analysis, ABS testing, suspension testing, navigation system testing, airbag testing, 4WD testing, transmission testing, vibration testing while the vehicle is driven, sensor signal analysis, etc.
•    Train car control testing
Element control testing, inverter motor control testing, train operation control testing, etc.; brake characteristics and vibration analysis, etc.

3. Manufacturing and machinery
•    Control analysis in steelmaking, chemical, and other types of industrial plants
Analysis of instrumentation signals, analysis of solenoid valve and control system malfunctions
•    Plant equipment maintenance, motor and bearing vibration analysis
•    Hydraulic equipment pressure testing
•    Analysis of characteristic vibration frequencies of various types of equipment and machinery
•    Analysis of control systems for injection molding machines
•    Diagnosis of malfunctions affecting rotating equipment
•    Measurement of welding currents
•    Analysis of malfunctions affecting automated equipment

4. Maintenance
•    Elevator acceleration testing and analysis of electrical control malfunctions
•    Analysis of rotating equipment

5. Other
•    Material testing (compression, tension, load, vibration, and impact testing, etc.)
•    Medical (recording of electrical activity of the heart, measurement in combination with various types of medical equipment)
•    Construction and civil engineering (vibration and impact testing; analysis of characteristic vibration frequencies of various objects)
Chemical (explosive testing of gunpowder and pressure analysis)

Example: Measuring the input and output characteristics of DC power supply

Objective:
To measure the rising time in output after the power supply switch is activated

Key considerations:
A level trigger should be activated at the rising edge of the primary input when the power switch is turned on.

1)    Setting recording length
Since we want to capture data for about 2 s, set the shot length (recording length) to 20 div. at 100 ms/div.

2)    Setting input range
Since the primary side of the circuit is 100 V AC, which yields a P-P value of 282 V, set channel 1 to 100 V/div. Since the secondary side is 5 V DC, set channel 2 to 1 V/div.

3)    Making trigger setting
Since the voltage will change from 0 to 100 V (RMS) when the switch is turned on, set the trigger level to a rising slope that is greater than 0 V. This explanation will use a setting of 10 V.

4)    Setting the trigger start point (Pre-trigger)
Since we want data after the switch is turned on, use a pre-trigger setting of 10%.

5)    Selecting trigger mode
Since we need only one measurement, use single mode.

6)    Data printing setting
If you wish the instrument to print data automatically when the trigger activates, turn on automatic printing on the status (settings) screen. If you wish to automatically save data in external memory, select the type of media and select the data format (binary or text). If you capture data on the screen even though automatic printing is off, you can record or print it later using the PRINT key, so turn this setting off.

7)    Setting [Waiting for pre-trigger]
Check the input cord connections and press the START key. If the display indicates that the instrument is in the trigger standby state, it has been set up properly.

8)    Recording
Turn on the power supply switch. If the instrument has been configured correctly, measurement will end once acquisition of the waveform data is complete.

Example: Measuring the input and output characteristics of DC power supply 2

Objective:
To measure the fall time in output after the power supply switch is activated

Key considerations:
Configure a trigger so that it is activated by the falling edge of the AC power supply. Since the level trigger would not be activated for channel 1, use either a voltage drop trigger with peak value detection or set up a trigger to activate at the falling edge of the DC output voltage level. If you have a line-use logic probe, you can also set up a trigger to activate when the input logic level switches from 1 to 0. This explanation will focus on the measurement procedure when using a voltage drop trigger. Once you understand how to use this voltage drop trigger, you will be able to measure momentary outages and momentary voltage drops affecting AC power supplies.

■ Measurement using a voltage drop trigger
1) Setting recording length
Select the voltage drop trigger for channel 1 and set it to 5 V.

2) Setting input range
Since the primary side of the circuit is 100 V AC, which yields a P-P value of 282 V, set channel 1 to 100 V/div. Since the secondary side is 5 V DC, set channel 2 to 1 V/div.

3) Setting display positions
Set the 0 positions to around 60% and 10% so that channels 1 and 2 do not overlap. (The positions can be changed later after data has been acquired if the channel displays overlap, so it’s fine if they do.)

4) Making trigger setting
Select the voltage drop trigger for channel 1 and set it to 5 V.

5) Setting the trigger start point (Pre-trigger)
Since we want data after the switch is turned on, use a pre-trigger setting of 10%.

6) Selecting trigger mode
Since we need only one measurement, use single mode.

7) Data printing setting
（Same setting as example of "Measuring the input and output characteristics of DC power supply"）

8) Setting [Waiting for pre-trigger]
Check the input cord connections and press the START key. If the display indicates that the instrument is in the trigger standby state, it has been set up properly.

9) Recording
Turn off the power supply switch. If the instrument has been configured correctly, measurement will end once acquisition of the waveform data is complete.
*Same as Figure 5-1

■ Measurement using a line-use logic probe
Change the trigger condition settings and the logic channel display settings. Other settings are the same as described above.

1) Making trigger setting
Since the trigger will be activated based on logic input, set up a logic trigger. Using channel A1 [0.x.x.x] 4, set up the trigger so that it activates when channel A1 changes from 1 to 0.

2) Displaying logic channel
Display the logic channel A1 on the channel display screen.

3) The remaining settings are the same as those that were described in the previous section.

If you encounter a self-hold circuit such as a sequence control circuit that exhibits the issue of resetting when this approach is applied, you can analyze the issue, for example in the power supply circuit, by setting up a trigger to activate depending on whether or not the self-hold circuit has a voltage.

Example: Measuring starting current waveforms of motors

Objective:
Although instruments such as normal ammeters cannot be used to measure quantities such as instantaneous load current fluctuations or starting current, a Memory HiCorder can easily do so using waveform levels when utilized in combination with a clamp current sensor.

Key considerations:
Use a clamp current sensor and set up a trigger so that it is activated by the starting current. Use the scaling function so that current values can be read directly. Use a Hioki 9018 Clamp On Probe. The output rate will be 500 A AC  200 mV AC. You can also display trace cursors, use them to measure the maximum value and rush current time, and then use the parameter calculation function to calculate the maximum value.

1) Setting recording length
The recording length varies with the load, but here we will use a setting of 10 div. at 50 ms/div. to capture 0.5 s.

2) Setting input range
Since the clamp current sensor we’re using generates 200 mV AC output, set the 0 position to 50% using the 50 mV/div. range.

3) Making scaling settings
Select 2-point scaling on the system’s scaling settings screen and configure the settings as shown in Figure 5-12. Since use of the ENG setting in combination with scaling enables settings in units of 103 and 106, you can read values as indicative of units with a K, M, or G prefix.

Voltage　　Voltage values at 2-points
HIGH side　0.2000E+00　→　5.0000E+02　　[A]
LOW side　 0.0000E+00　→　0.0000E+00

4) Setting the trigger start point (Pre-trigger)
Since we need data after the trigger is activated, use a setting of 10%.

5) to 8)　(Sama as “Measuring the input and output characteristics of DC power supply”)

6) Maximum value calculation
Set parameter calculation to “ON” on the status (settings) screen and specify a calculation for channel 1 only. Since data remains, moving the flashing cursor to the parameter calculation “ON” setting will cause an “EXECUTE” button to be displayed on the function key GUI display. Press that button. The maximum value calculation result will be displayed on the screen.