3M 724 User Manual

0 (0)

Model 724 Work Station Monitor Instructions

Index
Section		Page
Safety Information..................................................................................................		3
1.	Theory of Operation ......................................................................................	4
2.	Installation of 3M™ Model 724 Monitor
	with Work Surface Ground Monitoring.........................................................	8
3.	Installation of Model 724 Monitor
	without Work Surface Ground Monitoring ...................................................	9
4.	Selection of Test Voltage and Resistance Limit ..........................................	12
5.	Mounting the 724 Monitor and 3M™ Model 732 Remote .........................	12
6.	Wrist Strap Connection ...............................................................................	13
7.	Fault Conditions ..........................................................................................	14
8.	3M™ Model 3057 Standby Jack.................................................................	15
9.	3M™ Model 733 Dual Conductor Remote Input Jack ...............................	15
10.	Installation of Model 733 Remote...............................................................	15
11.	Veriﬁcation Procedure for the Model 724 Monitor .....................................	16
12.	Speciﬁcations ..............................................................................................	19
13.	Parts Included ..............................................................................................	19
14.	Required Accessories and Optional Available Parts....................................	20
15.	Additional Wrist Strap Monitoring Information .........................................	20
16.	Warranty ......................................................................................................	21

Safety Information		America, obtain an appropriate AC adapter
Intended Use		meeting the speciﬁcations as stated in the
		user instruction manual (Section 12). Use
The 3M™ Model 724 Work Station Monitor
		of other components may cause improper
is designed to monitor the operation of two
		performances and/or unsafe conditions. For
wrist strap grounding systems and two
		use outside of North America, grounding of
work surfaces. This product has been
		the Model 724 Monitor is recommended
designed and tested for use with 3M™	Dual
		through a separate ground wire with ring
Conductor Wrist Straps and 3M Work

Surfaces Grounding Systems. For North America this unit is designed for use with an AC adapter included. Outside North

terminal supplied (Sections 2 and 3).

CAUTION

•Incorrect grounding of an operator may cause electrostatic discharge (ESD) damage to components or assemblies being handled. For proper grounding of the operator when using the 3M 724 Work Station Monitor, use of the three-prong AC adapter speciﬁed

in the user instruction manual or supplied ground wire with ring terminal is required.

•Verify that the electrical ground point is suitable. If you are not sure what a suitable ground is, contact a licensed electrician before installation.

Explanation of Symbols

– Caution: refer to user instruction manual.

– Operator(s) Wrist Strap Assembly Ground.

– Work Surface Ground.

– Electrical ground.

– Power input connector polarity (center negative).

– See user instruction manual for explanation of the indicator lamps.

Read and understand all safety information before operating this equipment.

Model 733	Model 724		Dual Conductor
Remote			Metal Wrist Strap*
	Work Station	Model 732
Splitter Kit
	Monitor	Remote	Dual Conductor

		Input Jack
			Fabric Wrist Strap*

Fig. 1 - Model 724 Work Station with dual conductor wrist strap assemblies and remote input jacks.

Section 1.

Theory of Operation

The 3M Model 724 Work Station Monitor (Fig. 1) is designed to monitor the operation of the wrist strap grounding systems of two operators. To accomplish this, it uses a DC current source to measure a loop electrical resistance. The system uses a special wrist band and ground cord that contain two independent elements.* The 724 monitor employs two selectable test voltages (9 and 16 volts) and resistance limits

(10 Megohms and 35 Megohms).**

It also monitors the grounding of up to two 3M work surfaces.

The Model 724 monitor performs a resistance measurement by applying an electrical current of less than 3 µ A approximately every 2.0 seconds for 0.2 of a second in duration. The path for the current is through one conductor of the ground cord that

contains a current-limiting resistor, through one side of the wrist band, through the skin of the wearer under the band, through the second side of the wrist band, through the second conductor of the ground cord that contains a current-limiting resistor, and ﬁnally back to the monitor.

Selection of Test Voltage and

Resistance Limit

Fig. 2 - Resistance/Voltage switch selection.

*Resistance values are ±15%

The Model 724 monitor allows for the selection of test voltages (9v or 16v) and resistance limits (10 Megohms or 35 Megohms). The additional ranges have been added to accommodate global Electrical Static Discharge requirements. Selection of the operating parameters are left up to the user’s discretion (See Section 4).

Operator Monitoring -

Single and Dual

Resistance High Operator

Resistance Low Operator

OK #1	OK #2	Resistance High
Operator	Operator	Work Surface

Fig. 3 - Face of Model 724

The wrist strap monitoring function is activated by plugging a wrist strap

dual conductor ground cord into either one of the jacks on the 3M™ Models 732/733 Dual Conductor Remote Input Jack. If the resistance of the wrist strap loop is within the limits of the selected range (1.5 Megohms to 10 Megohms or 1.5 Megohms to 35 Megohms)* on the Model 724 Monitor, the cord, the wrist band, and the contact to the arm of the wearer, it is considered to be functioning correctly. At this time, one of the (OK) green lamps (1 or 2) will be illuminated on the front of

the monitor.

If the resistance of the wrist strap loop is higher than the selected range

(10 Megohms or 35 Megohms)* on the

724 monitor, an (OK) wrist strap green lamp (1 or 2) extinguishes, and

a high wrist strap red lamp (H) illuminates with an audible alarm. This is an indication of a high resistance in the cord band, or poor contact between arm and band. If the resistance in the loop is under 1.5 Megohms,* it is an indication of a low resistance meaning one or both current-limiting resistors are bypassed. The low yellow lamp (L) will ﬂash and an (OK) green lamp

(1 or 2) will remain illuminated.

Caution

A low resistance condition can also be caused by touching a grounded object or by standing on a conductive surface.

The wrist strap of a second operator

is measured in the same way. Operators are identiﬁed by the two (OK) green lamps (1 & 2). However, the same high wrist strap red lamp (H) and low yellow (L) lamps illuminate when a fault is detected. The green lamp that extinguishes identiﬁes the operator that is experiencing the fault condition.

* Resistance values are ±15%

3M 733 Remote Splitter Kit purchased separately.

Voltage on Operator When Connected to the Model 724 Monitor

There is a concern about the voltage that is applied to an operator while they are connected to a monitor. Some of today’s electronic components are extremely sensitive to electrostatic discharge from a person (less than

10 volts). The following chart for

the Model 724 monitor illustrates the level of voltage that will appear on the operator under various resistance conditions.

Note:

For more information about wrist strap monitoring see Additional Wrist Strap Monitoring Information (Section 15).

Voltage on Operator when connected to the Model 724 monitor

Condition	9V-10 Megohms		9V-35 Megohms	16V-10 Megohms	16V-35 Megohms

No Skin Resistance		0.9V	0.9V	1.6V	1.6V

200K Ohm Skin
Resistance		1.0V	1.0V	1.8V	1.8V

Likely Case Before
Alarm		2.5V	3.6V	4.4V	6.4V

Worst Case Before
Alarm		4.5V	7.1V	8.0V	12.6V

Absolute Worst Case		9.0V	9.0V	16.0V	16.0V

Audible Alarm Tones

For wrist strap malfunctions the Model 724 monitor indicates a different tone for each operator-a continuous tone for #1 operator and a fast chirping beep for #2 operator. The volume of the wrist strap alarm is adjusted by selection of the internal DIP switch #1. For work surface malfunctions, a slow chirping beep is made. This alarm sound is turned on or off by selection of DIP switch #2. Switch #1 and #2 are accessible through a slot located in the bottom of the chassis.

Loud	On
	On

DIPswitchSwitch

Off

Switch#1

Switch #2

Soft

Model 724Bbottom Vview

Fig. 4 - Selected desired alarm options

Work Surface Monitoring

The Model 724 monitors its connection to ground and the grounding of a 3M ESD work surface. A loop resistance is measured from the monitor, through a 3M™ 2380 Monitor/Table Mat Cord to the work surface (Section 2), across the conductive layer of the work surface, through the grounding wire of the work surface to an electrical ground

and ﬁnally back to the monitor through the 724 grounding wire. If the resistance of the loop exceeds

3.7 Megohms* the work surface high red lamp (M) will illuminate and all green lamps will be extinguished. If DIP switch #2 is in the ON position (Fig. 4) the audible alarm will activate. If no ESD work surface is to be monitored, the 3M 2380 Monitor/Table Mat Cord and the ground wire of the 724 must be connected to an electrical ground (Section 3). This is done to ensure that the 724 is providing a ground connection for the operators. Again, if the loop resistance exceeds 3.7 Megohms the work surface high red lamp (M) will illuminate and the alarm will activate if selected.

Caution

The grounding wire from the work surface and the ground wire from the Model 724 monitor must be

attached to separate electrical grounds. The work surface monitoring function is active any time that the power supply for the monitor is plugged in.

Caution

Disconnect the 3M 2380 Monitor/ Table Mat Cord to prevent possible damage to the Model 724 monitor before testing the resistance of the work surface with a high voltage megohmmeter.

* Resistance values are ±15%

+ 14 hidden pages