Features and Functions

• 115 dB dynamic range for error free measurements.
• Impulse measuring range greater than 118 dB.
• Meets Type 0 and Type 1 standards worldwide including ANSI S1.4, IEC 651 and IEC 804.
• A and C weighting plus 16 user selectable bandwidths. Frequency range from 1 Hz (0.1 Hz unweighted peak) to 35 kHz (70 kHz optional with slightly reduced dynamic range).
• Triple detectors provide simultaneous rms, weighted-PEAK and unweighted-PEAK measurements.
• FAST, SLOW, and IMPULSE time constants for RMS detector.
• Dual statistical signal analyzers have been designed into the 870B. One analyzer stores a complete set of all long-term historic data. A second resettable statistical analyzer allows the operator to focus on shorter term events without interruption to long-term data gathering.
• Includes four channel general purpose data logger interface for devices measuring windspeed, wind direction, temperature, humidity, barometric pressure etc. Calibration, scaling and data inhibit functions are available for each channel.
• Built-in 25 hr battery, external battery or ac operation.
• Accumulates four different histories: Exceedances, Intervals, Short period Time History and Level Histogram.
• Sampling periods are user selectable from 32 samples per second to 42 minutes with memory capacity of up to 500,000 samples (standard) or >2 million samples (with optional memory).
• Selectively creates special exceedance reports when signal levels rise above a user-set trigger level and if the event duration is within a user-set time window (settable max).
• Each special exceedance report contains date and time of event, duration, event Leq, SEL and rapid sample time history during the event.
• System can automatically activate an audio tape recorder when signal level rises above user-set threshold.
• System can automatically activate alarms during signal exceedance and other events.
• Direct interfaces for printers, digital data recorders, analog tape recorders, computers, modems, and optional floppy-disk drives.
• Real-time printout of data during actual measurements.
• Dual RS-232 computer interface. Stores ten complete instrument setup registers, each with a descriptive name tag.
• Real-time operating system allows simultaneous gathering, viewing, printing, and downloading of data.
• Quartz clock/calendar system for time/date annotation and automatic time scheduled operation.
• Interfaces with optional Model 900 series preamplifiers and accessories.
• Interfaces with optional Model 2100 weather-proof outdoor microphone system for use in harsh environments and permanent installations.
• Stainless-steel case with optional weather-tight enclosures. 4-line, 160 character alphanumeric and graphics display. Visible in direct sunlight.
• Small size: 2 x 9 x 6 1/8 in (h x w x d) Lightweight: 3.75 lb, including batteries.
• EMI and RFI protected.
• 2-year warranty program.

Applications and Uses

• Statistical analysis of noise, vibration, and other signals
• As a Type 0 or Type 1 precision integrating sound level meter
• Aircraft and airport noise monitoring
• Traffic survey instrument
• Industrial noise monitor
• Community noise
• Employee noise exposure analysis
• Measurement of sonic boom, artillery, blast noise, automatic weapon fire, and other highly impulsive noise events
• Data logging vibration monitor using accelerometers
• Seismic and ground motion analysis using geophones

The Model 870B is a precision sound level meter that meets IEC 804 and ANSI S1.4 specifications for Type 0 accuracy when used with an appropriate microphone. It will meet A- or C-weighted, or unweighted noise measurement requirements anywhere in the world. In addition, the 870B contains features that insure better and more accurate measurements for a variety of situations. Some of these features are as follows:

115 dB Dynamic Range

A-Weighted Dynamic range of 115 dB not only simplifies measurements but virtually eliminates the age old problem of data outside the measurement range. With no range controls to set, sound level meter overloads and underranges are avoided. This assures valid measurements over the entire operating range. While such a large dynamic range may not always be needed for assessing the risk of hearing loss, such a range is essential for community and environmental noise, assessment of nonauditory effects, and studies on annoyance. This large range is also essential for accurate statistical analysis.

Adjustable Measurement Range

A variety of precision microphones are available with different sensitivities allowing the measurement of very small signals below 15 dBA, to signals as large as 200 dBA SPL. With the 115 dB dynamic range of the Model 870B, possible measurement ranges could be 15 to 130 dBA SPL up to 85 to 200 dBA SPL, for example. Signals as small as those found in quiet wilderness areas to closed-in blast testing can be measured accurately.

118 dB Pulse Range

This large pulse range assures the accurate measurement of all types of sounds. Noise from punch presses, stamping machines, etc., will be properly measured regardless of the background noise level or reverberation time of the work area. Many of the existing sound level meter products in the market create significant measurement errors because of their limited crest factor capability and their limited dynamic range.

Measures True RMS of Very Short Impulses

For a single 250 µs pulse (one cycle of a 4 kHz sinewave) the error is less than 0.5 dB, even when the background noise is 110 dB less than the amplitude of the measured pulse. The performance of the 870B represents a significant technological breakthrough in the accurate measurement of impulsive sounds. This capability ensures that normally difficult tests such as measuring the energy of a rifle shot in a quiet open field can be properly performed.

Flexible Features

The Model 870B contains the many features necessary to ensure that the instrument will provide quality measurements for many years. The software oriented design ensures that changing needs can never make the 870B obsolete. In addition, these features make the model 870B system adaptable to solving a large variety of sound measurement problems. Some of the key features that provide this flexibility are :

A, C and Linear Frequency Weighting

A, C, and Linear weightings are provided. C-weighting provides the data necessary to optimally use the Noise Reduction Rating (NRR) of hearing-protectors as well as giving the user some indication of when low frequency noise is a problem. The C-weighting can also be used for sonic booms. Linear weighting can be used for artillery measurements and other impulsive measurements.

Preselector filters

Bandwidth capabilities of the 870B extend from 1.0 Hz (0.1 Hz unweighted peak) to 35 kHz, spanning numerous measurement tasks from vibration and infrasound to ultrasound frequency ranges. To accommodate a variety of input transducers and measurement ranges, operator selectable high-pass and low-pass filters provide choices of 1, 5, 20, or 100 Hz for the low frequency cutoff; and 1, 16, 25, or 35 kHz for high frequency cutoff.

Use of the frequency preselector will allow optimization of transducers and the dynamic range and provides the ability to reject unwanted signals.

Overall/Current Data Accumulations

While the overall data is accumulated, a separate accumulator for the current measurements can be read and reset. The current accumulator can be used to measure LMAX, LMIN, Integrated Level, SEL, Dose and Projected Dose for time periods that are but a part of the overall measurements.

Multiple Detector modes

The Model 870B provides a full compliment of detector modes for the thorough analysis of all types of sounds. While the Slow detection mode is the currently used standard for most noise measurements, all output parameters of the 870B can be measured in terms of Fast or Impulse detection modes.

Using two parallel peak detection systems, weighted and unweighted, the 870B simultaneously takes both weighted and linear peak readings. The integrated level and peak samples can be stored simultaneously in a time history file and other reports. This enables the direct measurement of the true crest factor for any noise type.

3, 4, 5 or 6dB Exchange Rates

For the dose and integration measurements, four user selectable exchange rates are available which cover any current or projected need. Overall measurements can have different exchange rates from current measurements.

Criterion Levels and Threshold Levels Adjustable

These levels are adjustable in 1.0 dB steps anywhere in the measurement range. While many industrial measurements will use the 80 dB threshold and 90 dB criterion, many special applications are now feasible. For example, one might measure the contribution of sound above a 115 dB threshold to a daily Dose. Setting a 90 dB criterion level and a 115 dB threshold level would provide the percent of dose contributed by exposure of levels above 115 dB as seen below. These adjustments can also be made after the data is taken.

Logged Data Logic (LDL) Function

The Model 870B provides the capability to perform what if analysis on data stored in memory. Using an exclusive Logged Data Logic (LDL) the basic data generated by the 870B for Dose, SEL and Integrated measurements can be re-evaluated with mathematical exactness using new threshold limits, new criterions or different exchange rates in any combination. Even though prior data taken by the 870B used a particular threshold, criterion and exchange rate, the same data base can be accurately retabulated for any new combination of threshold, criterion and exchange rate. The LDL function can be used while running.

For environmental noise, the most likely threshold to change is the threshold contribution of aircraft noise. For example, Leq can be computed using several different values of threshold.

With the LDL Function, data taken by a Model 870B and stored in external data banks can be reloaded into a 870B. Re-evaluation against a new standard or a newly proposed law can be performed without retaking the data. This feature alone can save several man-years of effort if legal requirements or standards change. The LDL Function is a mathematically exact method and should not be confused with less accurate statistical approximation techniques.

Supports Various Microphone Options

The Model 870B can be used with any Larson•Davis microphones and 900 series preamps, as user selected polarization voltages of 0, 28, or 200 Vdc are available.

Measured and Calculated Data

The 870B provides an impressive array of measured and calculated data in a variety of formats. Data which are always provided include the following:

• Leq, SEL, Noise Dose and Projected Dose calculated independently by both the overall and the current statistical analyzers. Each uses its own values of Threshold, Criterion and Exchange Rate.
• LMIN, LMAX, LPEAK and LUNWEIGHTED PEAK, with date and times of each, as calculated independently by both the overall and current statistical processors.
• Leq, Ldn, CNEL
• Six selected values of Ln
• Counts of the number of times the measured levels have exceeded preselected exceedance levels of RMS1, RMS 2, Peak and Unweighted Peak.
• For each of the three A/D inputs, the average and extreme values, and the number of times the preset exceedance levels were exceeded.

Multiple History Formats

Each of the following detailed data outputs can also be selected as required:

• The first output is a Statistical Profile that provides Ln percentile levels from 1 percent to 99 percent in one percent increments, and level distribution graph.
• The second output is a Simple Time History which records an Leq and optiona Lpeak, Lmax, Luwpk, or current wind speed optional expanded memory. The sample period can be set from 1/32 of a second to 42 minutes.
• The third output is an Exceedance History in which each time the noise level exceeds a preset RMS or peak level, the Time, Duration, SEL, Integrated Level, Maximum Level, and Peak Level of the event are all saved. In addition to these values, a time history with an user adjustable period length will store from ten samples before the exceedance event occurs to ten samples after the event ends. Thus, a profile of an aircraft flyover can be measured.
• The fourth output is an Interval History in which the measurement period/interval can be set from one minute to over ninety-nine hours (hh:mm). For each interval the maximum, average (leq), and peak levels are provided. Additionally, six Ln levels for each interval are available with the Interval History measurement.

Enhanceable

The Model 870B provides many features that give the instrument the ability to be specially tailored to almost any sound measurement need. These features are:

Direct Printing Compatibility

Data can be printed directly to ASCII, EPSON, IBM, HP ThinkJet and HP LaserJet printers.

Fully Programmable and Computer Compatible

The 870B can communicate directly with external computers via the RS-232 interface provided standard. This computer hookup can serve to setup all the measurement modes of the 870B, provide real-time data measurement, or serve to transmit the stored data into a central computer file for immediate use or later analysis. The Baud-rate is programmable and can be set from 300 to 19200 baud. The firmware can be upgraded in the field.

Networking and Synchronous Data

The versatile unit allows a network of 870Bs to effectively compete with a large microphone array with respect to both cost and performance. The 870B contains a calendar and a real-time clock in each unit, which can be set by keyboard or by remote computer within one tenth second accuracy. This allows making simultaneous measurements by a network of 870Bs. The data from each unit could be read into a computer at the end of the measurement period and comparatively analyzed. Thus perimeter data can be captured simultaneously in both space and time by several 870Bs. The 870B has a unique daisy chain capability which allows one hundred (100) Model 870Bs to be connected to the same RS232 port on a computer. One of the key advantages of this approach is that a costly communication system can be avoided, making the overall system very portable and adaptable.

To avoid a mix-up each unit has its own digitally coded serial number which can be read out from the keyboard or through a computer.

Memory

The Model 870B comes standard with 512K of RAM for data storage. This will support approximately 6500 exceedance events, or nearly 9000 interval reports, or 250,000 simple history samples, or some combination of these. This is enough standard memory capacity to capture all the events of a typical airport for several weeks. In addition, the user will have the ability to store history data at either a one decibel resolution or at a one tenth decibel resolution. The benefit of the 1 dB resolution is that the number of history samples can be doubled.

If additional memory is needed, the Model 870B can be upgraded with optional memory to 2 MB RAM. This option provides 4 times the memory capability of the standard unit. Examples of the power of this extra memory are almost 12 days of 1 sec samples can be stored (24 days of 1 dB resolution samples), three months of airport events, or over 2 years of one minute Leqs.

Easy To Use

With so many features present in the Model 870B, a user might worry about the device being unduly complex. Yet it is very easy to learn and use for the following reasons:

Setup Registers

The Model 870B has been designed to allow the operator to customize and optimize all instrument features for each particular type of measurement application. To prevent having to reselect instrument functions when different types of measurements are performed, the 870B provides 10 separate setup registers to allow instant recall of all instrument functions. Only three keystrokes are required to configure for a totally different measurement! Each menu provides space for the operator to enter a descriptive title for the instrument setup such as the following:

1. AIRPORT NOISE ANALYSIS
2. SONIC BOOM TEST
3. COMMUNITY NOISE
4. TRAFFIC SURVEY

Settings are easily managed by computer software.

Alphanumeric Display and Keyboard

The four line, 40 character per line, display provides a data readout in plain English. The Model 870B provides a clearly annotated display, showing all pertinent measurement information simultaneously. Graphic capabilities of the display provides an annotated thermometer style bar-graph (1 dB resolution) with simultaneous 0.1 dB numeric readouts. Elapsed time is always presented on the LCD with the Dose and Equivalent Level measurements. This elapsed time provides positive feedback to the operator that the Dose measurement has started and is in process. In addition, a symbol of a animated person is always visible in any mode when data is being accumulated.

Keyboard layout provides a generous array of function keys and full alpha numeric capability to permit easy access to instrument setups and data. A scroll knob on the keyboard allows rapid access to all instrument functions as well as all stored data. Data may be accessed on-line even during system operation. Keyboard functions allow direct interface to peripheral equipment such as printers and external memory devices during or following data taking.

Auxiliary Inputs and Outputs

The Model 870B has been designed to communicate with it's surroundings.

Multiple input channels permit measurement of wind speed & direction, temperature, humidity, rainfall, and barometric pressure; or inputs can count traffic flow in 2 directions.

The output channels consist of AC out, DC out, and a pair of logic lines that can be used to turn external devices (such as a tape recorder) on or off. Tape recorders can be selectively and conditionally activated by the logic lines so that only desired acoustic signals are recorded. The DC and AC outputs have gain controls. The output logic line can be triggered by an exceedance report, a start of an interval report for a variable length of time, or by one of the DC inputs being exceeded. The logic line can also reflect the R/S state.

Battery Life

During measurements, the expected life, using the internal batteries, is up to 24 hours. With continuously powered memory, the 870B can be stored for months with the various modes selected, without memory loss. In addition, a battery change can be made without loss of mode selection or data. Thus the 870B needs to be programmed from the keyboard only once in most normal situations.

Tamper Protected

The keyboard and display can be set by the user to not respond to keyboard signals unless a special alpha-numeric access code is used. This prevents accidental or intentional keyboard input.

Automatic Measurements

A timer feature is provided to allow the user to set up to two start times, two stop times, the start date and the stop date. Three modes allow for a single data run, one data run per day or two data runs per day.

Serviceable

Rugged

A specially shielded metal case with sealed keyboard typify the extra rugged construction of the Model 870B. Temperature and humidity stability are excellent. In addition, the measurement microphone and cable connections are designed to take the heavy use of the industrial setting.

Memory Usage

The 64 K RAM (expandable to 256 K) is used to store data for the Run/Stop Log, and the Daily, Interval, Time and Exceedance Histories. The Histogram data use a separate memory, and does not affect the amount of available memory. The History memory usage is as follows:

1. Run/Stop Log
   16 bytes per RUN, STOP, PAUSE, CONT or MARK
   
   
2. Daily History
   65 bytes/day (or per STOP) Interval History
   
   
3. This report can be formatted to be with or without the six preselected Ln values, and with or without data from the three A:D inputs. The interval period is selected as hours and minutes.
   
   A:D Data Ln's With Without

   With	61	43
   Without	52	34
   Table 1: Bytes per Interval Record

   
   
4. Time History
   When formatting the Time History, one selects the resolution to be either 0.1 dB or 1.0 dB, and chooses to retain both the integrated level and peak for each period, or only the integrated level. The period may be 10.0, 1.0 or 1/32 second, and integer multiple of these, up to a multiplier of 255. For example, with a UNIT setting of 10 seconds, and a period of 180, a new sample will be produced every 1800 seconds or every 30 minutes.
   
   Data Retained Resolution 0.1 dB 1.0 dB

   Integrated Level & Peak	4	2
   Integrated Level Only	2	1
   Table 2: Bytes per Period

   
   
   
5. Exceedance History
   This report can be formatted to be with or without exceedance time histories, and with or without data from the three A:D inputs. The actual amount of memory used for a time history will depend upon the sample period and the exceedance duration. The ten samples occurring prior to the exceedance are stored in addition to those occurring during the exceedance, up to a maximum of 128. The sampling period is set as n/32 seconds, where n is an integer between 1 and 255. The resolution is always 1.0 dB.
   A:D Data Time History With Without

   With	46-164	36
   Without	40-158	30
   Table 1: Bytes per Interval Record

Setup

For a specific measurement project, select those histories which are required, then choose the formatting parameters (interval period, time history period and resolution, whether or not to have Ln's, analog to digital (A:D) input data, etc.) such that the total memory requirements do not exceed the available memory.